Establishment of rational parameters of temperature of working liquid in the hydraulic drive of the excavator of the fourth dimensional group at different equipment

The article considers the hydraulic drive of a modern excavator on which the influence of the working fluid temperature on the power is established, depending on the technical condition of the hydraulic elements. Studies have shown that new pumps and which have operating wear, have different rational temperature of the working fluid. It is impossible to imagine modern construction machines without equipping them with a hydraulic drive. The operation of the hydraulic drive largely determines the efficiency of operation of both a single machine and the entire fleet, which consists of new and old machines . The efficiency of hydrated machines is ensured in their design, manufacture, and operation, where an important role is played by the parameters of the working fluid: the degree of its contamination and temperature (viscosity). The influence of the temperature of the working fluid on the efficiency of the hydraulic drive and the ability to control the efficiency of the hydraulic drive with the help of temperature have not been studied enough. One of the promising areas in determining the rational temperature of the working fluid is the development of new designs of heat exchangers, heaters, diagnostic devices, which will be able to assess the technical condition of individual elements and the hydraulic drive as a whole. Establishing a rational temperature of the working fluid as a necessary parameter of the hydraulic system is mandatory when using modern methods to increase the efficiency of operation, maintenance and repair of hydraulic drives. With increasing temperature of the working fluid, its viscosity decreases and the loss of pressure and power in the mains of the hydraulic drive. However, this increases the internal flow of hydraulic units, which leads to an increase in power loss. Studies have shown that new pumps and which have operational wear, have different rational temperature of the working fluid. At rational values of temperature to the hydraulic motor the worn out pumps can give almost twice more power, than at 50 ° C, recommended for new pumps. The driving power of the pump, thus, practically does not change.

Structural stabilities, electronic structures, photocatalysis and optical properties of γ-GeN and α-SnP monolayers: a first-principles study

Exploring two-dimensional materials with excellent photoelectricity properties is of great theoretical significance and practical value for developing new photocatalysts, electronics and photonic devices. Here, using first-principle calculations, we designed and analyzed systematically a series of α, β and γ phase structures of two-dimensional group IV-V monolayers (IV-V, IV = C, Si, Ge, Sn, Pb；V = N, P, As, Sb, Bi), most of them are semiconductors. Among them, γ-GeN and α-SnP monolayers with thermodynamic and kinetic stability (at 300K) have been further studied due to their wide range of energy band gaps (γ-GeN: 2.54 eV, α-SnP:1.34 eV). The two band gaps are greater than the free energy for water splitting (1.23 eV), which are crucial for photocatalytic decomposition of water. The γ-GeN and α-SnP monolayers present excellent photocatalystics properties in PH=0/7 and PH=10 environments, respectively. Moreover, both of the monolayers show strong light absorption coefficients greater than 105 cm-1 in the visible and ultraviolet regions. In addition, it is found that the band edge positions and band gap sizes of γ-GeN and α-SnP monolayers can be regulated by biaxial strain. Benefitting from the wide selection of energy band gaps and high absorption coefficients, the γ-GeN and α-SnP monolayers are the next generation of promising candidate materials for photocatalysts, nanoelectronics and optoelectronics.

Four-dimensional Einstein manifolds with Heisenberg symmetry

We classify Einstein metrics on $$\mathbb {R}^4$$ R 4 invariant under a four-dimensional group of isometries including a principal action of the Heisenberg group. We consider metrics which are either Ricci-flat or of negative Ricci curvature. We show that all of the Ricci-flat metrics, including the simplest ones which are hyper-Kähler, are incomplete. By contrast, those of negative Ricci curvature contain precisely two complete examples: the complex hyperbolic metric and a metric of cohomogeneity one known as the one-loop deformed universal hypermultiplet.

Gravitational edge modes, coadjoint orbits, and hydrodynamics

The phase space of general relativity in a finite subregion is characterized by edge modes localized at the codimension-2 boundary, transforming under an infinite-dimensional group of symmetries. The quantization of this symmetry algebra is conjectured to be an important aspect of quantum gravity. As a step towards quantization, we derive a complete classification of the positive-area coadjoint orbits of this group for boundaries that are topologically a 2-sphere. This classification parallels Wigner’s famous classification of representations of the Poincaré group since both groups have the structure of a semidirect product. We find that the total area is a Casimir of the algebra, analogous to mass in the Poincaré group. A further infinite family of Casimirs can be constructed from the curvature of the normal bundle of the boundary surface. These arise as invariants of the little group, which is the group of area-preserving diffeomorphisms, and are the analogues of spin. Additionally, we show that the symmetry group of hydrodynamics appears as a reduction of the corner symmetries of general relativity. Coadjoint orbits of both groups are classified by the same set of invariants, and, in the case of the hydrodynamical group, the invariants are interpreted as the generalized enstrophies of the fluid.

Anisotropic to Isotropic Transition in Monolayer Group-IV Tellurides

Monolayer group-IV tellurides with phosphorene-derived structures are attracting increasing research interest because of their unique properties. Here, we systematically studied the quasiparticle electronic and optical properties of two-dimensional group-IV tellurides (SiTe, GeTe, SnTe, PbTe) using the GW and Bethe–Salpeter equation method. The calculations revealed that all group-IV tellurides are indirect bandgap semiconductors except for monolayer PbTe with a direct gap of 1.742 eV, while all of them are predicted to have prominent carrier transport ability. We further found that the excitonic effect has a significant impact on the optical properties for monolayer group-IV tellurides, and the predicted exciton binding energy is up to 0.598 eV for SiTe. Interestingly, the physical properties of monolayer group-IV tellurides were subject to an increasingly isotropic trend: from SiTe to PbTe, the differences of the calculated quasiparticle band gap, optical gap, and further exciton binding energy along different directions tended to decrease. We demonstrated that these anisotropic electronic and optical properties originate from the structural anisotropy, which in turn is the result of Coulomb repulsion between non-bonding electron pairs. Our theoretical results provide a deeper understanding of the anisotropic properties of group-IV telluride monolayers.

Anisotropy of Unstably Stratified Near-Surface Turbulence

Classic Monin–Obukov similarity scaling states that in a stationary, horizontally homogeneous flow, in the absence of subsidence, turbulence is dictated by the balance between shear production and buoyancy production/destruction, whose ratio is characterized by a single universal scaling parameter. An evident breakdown in scaling is observed though, through large scatter in traditional scaling relations for the horizontal velocity variances under unstable stratification, or more generally in complex flow conditions. This breakdown suggests the existence of processes other than local shear and buoyancy that modulate near-surface turbulence. Recent studies on the role of anisotropy in similarity scaling have shown that anisotropy, even if calculated locally, may encode the information about these missing processes. We therefore examine the possible processes that govern the degree of anisotropy in convective conditions. We first use the reduced turbulence-kinetic-energy budget to show that anisotropy in convective conditions cannot be uniquely described by a balance of buoyancy and shear production and dissipation, but that other terms in the budget play an important role. Subsequently, we identify a ratio of local time scales that acts as a proxy for the anisotropic state of convective turbulence. This ratio can be used to formulate a new non-dimensional group. Results show that building on this approach the role of anisotropy in scaling relations over complex terrain can be placed into a more generalized framework.