Positron beams, both polarized and unpolarized, are identified as important ingredients for the experimental programs at the next generation of lepton accelerators. In the context of the hadronic ...physics program at Jefferson Lab (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic structure of nucleons and nuclei, in both the elastic and deep-inelastic regimes. For instance, elastic scattering of polarized and unpolarized electrons and positrons from the nucleon enables a model independent determination of its electromagnetic form factors. Also, the deeply-virtual scattering of polarized and unpolarized electrons and positrons allows unambiguous separation of the different contributions to the cross section of the lepto-production of photons and of lepton-pairs, enabling an accurate determination of the nucleons and nuclei generalized parton distributions, and providing an access to the gravitational form factors of the energy-momentum tensor. Furthermore, positron beams offer the possibility of alternative tests of the Standard Model of particle physics through the search of a dark photon, the precise measurement of electroweak couplings, and the investigation of charged lepton flavor violation. This document discusses the perspectives of an experimental program with high duty-cycle positron beams at JLab.
The surface layer determines the physical properties of aviation materials and, based on these properties, the calculation of surface energy anisotropy can be implemented. Moreover, the value of the ...surface energy determines the service time and the destruction of aircraft structures surface layer, while the surface layer thickness determines the distance at which this process usually takes place. In this work, a new atomically smooth crystal empirical model is built without considering the surface roughness. This model can be used to theoretically predict the surface energy anisotropy and surface layer thickness of metals and other compounds, in particular the aviation materials. The work shows that the surface layer of an atomically smooth metal, like other compounds, consists of two nanostructured layers: d(I) and d(II). Having sufficient accuracy, the proposed model would allow the prediction of aviation materials performance properties without the need for ultrahigh vacuum or other complicated theoretical methods to analyze the surfaces of nanosystem atomic structures.
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Kinetics of thymol release from 500 μm thick poly(ethylene oxide) and low-density polyethylene, in which thymol is in one of the possible states (fine dispersion of droplets, fine dispersion of ...crystals, or solution in the amorphous regions of semicrystalline polymer) has been studied. The experiments by means of gravimetry have revealed that the release of thymol in these states has been complete within 120, 240, and 780 h, respectively. Scanning electron microscopy data have demonstrated that initially monolithic poly(ethylene oxide) film has turned porous during thymol release, in contrast to the polyethylene film, which has been initially porous and has become monolithic. The reasons of the marked behavior have been discussed in view of the poly(ethylene oxide)–thymol and low-density polyethylene–thymol state diagrams, the former one being obtained for the first time using an optical method. The obtained results have demonstrated the importance of the physical state of the active component during its controlled release from the semicrystalline polymer matrix.
The article reviews the existing methods for determining the surface energy of solids. Each of the methods described is practically limited to either temperature or values that are experimentally ...determined with low accuracy. A method is proposed for determining the surface energy of a solid on the basis of the dimensional dependence of its physical properties (magnetic permeability, luminescence intensity, thermal conductivity, etc.). The surface energy of some nitrides, borides and carbides is determined. Its magnitude is much larger than the surface energy of pure metals. The critical radius of nitrides, borides and carbides is calculated, from which the direct Hall-Petch effect is reversed.
The article presents the results of the studies related to the development of hardening, antifriction, heat-resistant, corrosion-resistant coatings. There have been considered the models of ...concentration supercooling associated with the presence of a radial concentration gradient of metal nitride impurity; Benard cells, the occurrence of which is caused by the presence of a vertical temperature gradient; a cellular dislocation structure associated with the presence of plastic deformations in the coating; the emergence of auto-waves in the most diverse environments, including living beings. From the studies presented in the work, it follows that self-organization of forming coatings can occur only under conditions of a large value of the surface energy.
The influence of the cutting conditions on the life of quadrilateral cutting heads in the rough cutting of conical gears with circular teeth is investigated experimentally.
Abstract
In this article, the microhardness and wear resistance of the high-entropy FeCrNiTiZrAl alloy are studied on model specimens and on turbine blades made of 20Kh13 steel. The alloy was made by ...mechanical alloying and subsequent annealing in a vacuum furnace. The study showed that the obtained alloy is a high-entropy alloy with a microhardness μ = 740 HV, which is at the level of the microhardness of metallic glasses, but 2-3 times higher than the microhardness of stainless steels. The friction coefficient of the FeCrNiTiZrAl coating is k = 0.06, which is 10 times less than the friction coefficient of the titanium nitride coating (k = 0.65). The wear resistance of the high-entropy FeCrNiTiZrAl coating is much higher than that of stainless steels, and it leads to the fact that the cost of titanium nitride coating on turbine blades is 2 times higher than the cost of FeCrNiTiZrAl coating, that is, the economic effect is obvious.
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