On the question of the appointment of separate parameters of the roadheaders gathering-stars loading organs

Most modern roadheaders of selective action are equipped with loading devices with gathering-stars, which have a simpler drive design and increased reliability. As a result of the experimental studies carried out at SRSPU (NPI), it was found that under certain conditions, it is possible to transfer large lump material of a pile into a fluidized state, which reduces the energy consumption of material loading. An increase in the number of beams of the gathering-stars reduces the influence of the other parameters of the loader. Analysis of the process of interaction of the gathering-star’s beam with the receiving conveyor’s side edge to avoid jamming of the picking gathering-star by a lump of material with the implementation of high dynamic loads, it is necessary to set the gathering-beams at an angle of at least 60 degrees against rotation.

A side-edge frame dual-band eight-element MIMO antenna array for 5G handset

In this paper, a dual-band 8 × 8 multi-input multi-output (MIMO) array antenna operating in 3.5 GHz band (3400–3600 MHz) and 5.5 GHz band (5150–5925 MHz) for 5G mobile handset is presented. The proposed hybrid antenna includes a comb-shaped monopole and an L-shaped open slot antenna which are symmetrically located on the inner surface of the side-edge frame of smartphone. Pattern diversity is achieved that can mitigate envelope correlation coefficients (ECCs) and improve the MIMO system performances. The prototype of proposed dual-band eight-element MIMO antenna is fabricated and experimentally measured. The results show that isolation <−10 and <−15 dB, respectively in the lower band and high band without any additional decoupling element are achieved and the desired bands are satisfied under the condition of −6 dB impedance matching. Moreover, the essential parameters for evaluation of the MIMO system performance such as the ECC, mean effective gain (MEG), and ergodic channel capacity are calculated. Furthermore, the influence of user's hand on the radiation characteristics of proposed MIMO antenna are also investigated and discussed. Based on the result, the proposed MIMO antenna is a good candidate for use in future 5G applications.

ТЕОРЕТИЧНА МОДЕЛЬ ФОРМУВАННЯ ДВОВИМІРНИХ НАНОСТРУКТУР ВЕРТИКАЛЬНОГО ГРАФЕНУ ПІД ДІЄЮ ПЛАЗМИ

Vertically oriented graphene nanostructures have been grown for more than decade, but the mechanisms of their formation are still unclear. A multifactor model is proposed, which is verified by comparison with experimental data and describes the processes of growth of the structure of vertical graphene in plasma. The role of chemical and physical processes that cannot be directly characterized by available experimental methods, such as surface diffusion of adatoms and radicals under the action of ions, has been studied. Ion bombardment is a key factor that significantly accelerates the growth rate through the formation of surface defects and, consequently, increases the energy of surface adsorption. Hydrocarbon radicals formed on the substrate under the bombardment diffuse to the graphene nanosheets and serve as the main source of the construction material. Thus, the leading role in the formation of vertical graphene belongs to surface diffusion, rather than direct deposition from the gas phase. The temperature of the sample is also an important parameter, which affects the growth process according to the following mechanism: at low temperatures the adsorption from the gas phase is more intense, but the diffusion processes are slowed down; elevated temperatures have the opposite effect. The surface density of graphene nanosheets, which can be controlled at the stage of nucleation, strongly affects the height of the structure due to the redistribution of ion fluxes during the growth: as the nanosheets grow, the ion current density decreases to the side edge of the sheet and increases to the upper edge. This process leads to a decrease in the ion current density at the side edge of the nanosheet, and, as a consequence, to a change in the dependence of the graphene sheet length on time: from a saturated curve or a quasilinear time dependence to a parabolic dependence. The assumption of surface diffusion of hydrocarbon radicals as the dominant growth mechanism is consistent with existing experimental data; these results confirm the physical model, and also bring a deeper understanding of the physics of growth of vertical graphene.

Features of the wear of the working bodies of the Viking tillage unit

It is shown that the most uniform wear of the bit blade occurs when soil particles move perpendicular to the blade edge. It has been determined that the width of the edge affects the traction resistance of the body, the penetration ability, and the strength of the blade. It has been found that in case of loamy soils, the optimal width of the blade part is in the range between 70 and 80 mm at an acute angle of 50 degrees between the bit blade and the side edge.

Investigation of the Wear Behavior of Abrasive Grits in a Dry Machining Inconel 718 Narrow-Deep-Groove with a Single-Layer Cubic Boron Nitride Grinding Wheel

The wear behavior of a single-layer electroplated cubic boron nitride (cBN) grinding wheel was investigated in creep feed profile grinding Inconel 718 narrow-deep-groove with a width of 2 mm. In this paper, the protrusion height of cBN grits on the side edge of the grinding wheel was measured by three-dimensional optical profiler, and a scanning electron microscope was used to detect the topography of worn cBN grit and the nickel bonding layer. The investigation results indicated that the steady wear stage of the grinding wheel shared more than 84.6% of the wheel lifespan, and the machining precision of the grinding wheel was kept at a high level. The fracture mode of the cBN grit was proven to be cleavage. The source of the cleavage cracks was observed on the surface of wear flat or the side surface of the cBN grit. The holding strength of cBN grit could be weakened due to the joint surface breakage, the displacement of grit, or the cracks of the nickel bonding layer. The transition layer was contributed to the decrease of the bonding strength. Severe macro fractures and the concentration of pulled out grits were observed on the transition edge and the inner area of the side edge, separately. This study provides a deep understanding of the wear mechanism of a single-layer electroplated cBN grinding wheel.

Two new species of the genus Xya Latreille, 1809 (Orthoptera, Tridactyloidea, Tridactylidae) from Yunnan with a key to all Xya species in China

This contribution to the taxonomy of Xya Latreille, 1809 (Orthoptera, Tridactyloidea, Tridactylidae) adds descriptions and photographic illustrations of two new species: Xya xishangbannasp. nov. and Xya yunnanensissp. nov. from Xishuangbanna, Yunnan Province, China. Xya xishangbannasp. nov. can be diagnosed by the shiny dark brown hind femora, and the epiproct with a shallow bottom of the middle “v-shaped” crack in the upper part and straight sides; Xya yunnanensissp. nov. can be diagnosed by the compound eye bearing no narrow band along the inner margin, and the epiproct with the bottom of the side edge with a sharply angled protrusion and a narrow lower anchor-shaped base less than 1/2 the width of the upper one. Distributional information and bionomics for these two new species and photos for the habitat are given. A key to all Chinese species of Xya is provided.