Technical Physics Letters最新文献

Abstract—The growth mechanism of monolayer on the top facet of Ga-catalyzed GaAs and GaP nanowires is investigated. Within the framework of a theoretical model, the maximal monolayer coverage due to the material in the catalyst droplet, the nanowire growth rate and the content of group V atoms in the droplet are found depending on the growth conditions. The estimates of the phosphorus re-evaporation coefficient from neighboring nanowires and substrate are obtained by comparing the theoretical and experimental growth rate of Ga-catalyzed GaP nanowires.

Abstract

The functionalization of multi-walled carbon nanotubes in He:O plasma is investigated. It is shown that plasma treatment leads to the removal of defective outer graphene layers and their fragments due to oxidation. It is established that the surface of functionalized multi-walled carbon nanotubes contains numerous uncoordinated carbon atoms and oxygen-containing functional groups. The preservation of the structure of the internal graphene layers of nanotubes and the formation of broken chemical bonds ensure a decrease in electrical resistance. At the same time, there is a narrowing of the distribution of electrical resistance values of nanotube ensembles.

Abstract

The properties of c-oriented thin films of Sr_0.5Ba_0.5Nb₂O₆ grown on a Si(001) (p-type) substrate with a pre-deposited Ba_0.2Sr_0.8TiO₃ layer were studied using scanning probe microscopy and dielectric spectroscopy. It is established that the Sr_0.5Ba_0.5Nb₂O₆ films are characterized by low surface roughness (less than 6 nm) and average crystallite size of ~93 nm. It is shown that there is spontaneous polarization in the film directed from its surface to the substrate, which causes the manifestation of the field effect for the case of the Si substrate with p-type conductivity without the external field effect. Differences in the magnitudes of the surface potential signal for regions polarized by an external electric field of different polarities (+10 and –10 V), as well as in their relaxation to the initial state, are revealed. The reasons for the established patterns are discussed.

Abstract—An experimental method was developed to determine losses in microstrip and coplanar transmission lines for devices operating in the frequency range of 77–81 GHz. The parameters of the scattering matrices are obtained using a vector network analyzer and frequency upconverters. The calculation of losses in waveguide-coplanar and coplanar-microstrip adapters is made.

Abstract

The results of numerical investigation of the hydrodynamic drag of a slit microchannel with a textured wall surface, as well as of the pressure drop in such a channel and the effective slip length on the wall for various Reynolds numbers, are presented. The channel height was 10 μm, and the length varied from 25 to 500 μm. It was found that the pressure drop in the textured microchannel was less than in a conventional one at any length. The dependences of the relative pressure drop, friction factor, and effective slip length on the Reynolds number were obtained for various channel lengths. A correlation that describes the dependence of the relative pressure drop on the Reynolds number for small channel lengths was proposed. The friction factor was described by a correlation expressed as 20/Re.

Abstract—Temporal characteristics of the localized damage development initiated by a short-time impact pointed loading of SiC ceramics which is widely applied as a protective material against the shock action upon engineering constructions and people were investigated. The statistics of crack nucleation and relaxation was studied with the methods of acoustic emission and electromagnetic emission, correspondingly. It was shown that the length of intervals between microcrack nucleations follows a power law specific to cooperative phenomena. The time distribution of decaying electric charges which appear on impact-induced crack edges and annihilate after the passage of impact wave was, in contrast, linear. The temporal pattern of the crack relaxation permitted identifying two sets of newly formed damages that are the tiny cracks localized in the grain bulk and those that interconnect grains.

Abstract—Wavelet analysis is one of the most efficient methods of the informative signals characteristics investigation. First shown the possibility of informative signals wavelet processing by means of the acousto-optic processor with time integration. The possibility of the realization of both power spectrum calculation and performance of wavelet transform of bioelectric signals in the real time mode has been proved. The analysis is listed which describes its operation in different modes.

Abstract

The problem of synthesis of the three-link stepped Chebyshev’s microwave filter is reduced to two independent fourth-degree equations, including a single link wave impedance as unknown. The solution of Descartes—Euler is applied to these equations. It is proved that, in case wave impedances of extreme links are equal, the problem of the filter synthesis has two solutions. Identical phase-frequency responses correspond to these solutions. It is proved that for each link a product of the wave impedances relating to these solutions is equal to a square of the wave impedance of the transmission line including the filter.

Abstract

A method to define the characteristic phases in the behavior of unidirectionally coupled systems located near the boundary of the generalized chaotic synchronization regime onset based on calculating the probability of the synchronous regime observation in an ensemble of coupled systems is proposed. Using the example of unidirectionally coupled Rössler systems in the band chaos regime, we have shown its efficiency in comparison with other known methods for detecting the characteristics of intermittent generalized synchronization.

Abstract

The degree of influence of the electromagnetic field on oil dispersed systems depends on the dielectric properties of these systems, in particular oil. Dielectric properties of oil depend on the content of high molecular weight polar components: asphaltenes and resins. In this regard, a study was carried out of the dielectric properties of oil in the radio-frequency range, depending on the content of asphalt–resinous substances in it. The obtained results of experimental studies show the correlation of dielectric parameters with the ratio of the content of resins and asphaltenes in oil.