Scalar Density Research Articles

Влияние электроимпульсной обработки на структуру и твердость криокатаного алюминия

The influence of the energy of electric pulse treatment (EPT) in the range of integral current densities (Kj) from 0.06 ×105 to 0.29 ×105 A2s / mm4 on the structure and hardness of coarse-grained high-purity Al, isothermally rolled up to a total strain of 90 % at a liquid nitrogen temperature, was studied. It was found that EPT with an energy up to Кj = 0.104 ×105 A2s / mm4 practically did not affect the microhardness obtained in the cryorolled aluminum (45 – 50 HV). An increase in the EPT energy to Кj = 0.121×105 A2s / mm4 led to a rapid drop of the hardness to 30 HV followed by its gradual stabilization near 25 HV at higher Кj values. It was established that an enhanced microhardness of rolled Al resulted from formation of a well developed cellular structure with a crystallite size of about 2 μm, containing less than 10 % of ultrafine grains of about 4 μm in size. The minor hardness changes after EPT with Кj up to 0.104 ×105 A2s / mm4 were related to occurrence of recovery and continuous recrystallization, resulted only in improving the deformation structure without noticeable changes in its type and the crystallite sizes. Therewith the softening caused by a partial decrease in the scalar dislocation density and the microdeformation of the crystal lattice was compensated by increasing the high angle boundaries fraction. At EPT with Кj = 0.121×105 A2s / mm4, the deformation structure was severely replaced by the fine-grain recrystallized one with the grain size of 19 μm, and resulted in the loss of the strenthening effect, caused by rolling. With further increase in the EPT energy, an extensive grain growth was observed, leading to the formation of a non-uniform structure grains and to appropriate material softening, owing to the grain coarsening. It was concluded that the restoration processes that took place during EPT were similar in nature to those that occur during furnace annealing of heavily deformed materials. Therewith, the short time of the thermal exposure on the deformed metal during EPT was compensated by high applied energies.

Ratio of flavour non-singlet and singlet scalar density renormalisation parameters in N_mathrm {f}=3 QCD with Wilson quarks

We determine non-perturbatively the normalisation factor r_{mathrm{m}}equiv Z_{mathrm{S}}/Z_{mathrm{S}}^{0}, where Z_{mathrm{S}} and Z_{mathrm{S}}^{0} are the renormalisation parameters of the flavour non-singlet and singlet scalar densities, respectively. This quantity is required in the computation of quark masses with Wilson fermions and for instance the renormalisation of nucleon matrix elements of scalar densities. Our calculation involves simulations of finite-volume lattice QCD with the tree-level Symanzik-improved gauge action, N_{mathrm{f}}= 3 mass-degenerate {mathrm{O}}(a) improved Wilson fermions and Schrödinger functional boundary conditions. The slope of the current quark mass, as a function of the subtracted Wilson quark mass is extracted both in a unitary setup (where nearly chiral valence and sea quark masses are degenerate) and in a non-unitary setup (where all valence flavours are chiral and the sea quark masses are small). These slopes are then combined with Z equiv Z_{mathrm{P}}/(Z_{mathrm{S}}Z_{mathrm{A}}) in order to obtain r_{mathrm{m}}. A novel chiral Ward identity is employed for the calculation of the normalisation factor Z. Our results cover the range of gauge couplings corresponding to lattice spacings below 0.1,fm, for which N_{mathrm{f}}= 2+1 QCD simulations in large volumes with the same lattice action are typically performed.

Early Mass-varying Neutrino Dark Energy: Nugget Formation and Hubble Anomaly

Abstract We present a novel scenario in which light (∼few eV) dark fermions (sterile neutrinos) interact with a scalar field as in mass-varying neutrino dark energy theories. As the eV sterile states naturally become nonrelativistic before the matter–radiation equality (MRE), we show that the neutrino–scalar fluid develops strong perturbative instability followed by the formation of neutrino nuggets, and the early dark energy (EDE) behavior disappears around MRE. The stability of the nugget is achieved when the Fermi pressure balances the attractive scalar force, and we numerically find the mass and radius of heavy cold nuggets by solving for the static configuration for the scalar field. We find that for the case when dark matter nugget density is subdominant and most of the EDE go into scalar field dynamics, it can in principle relax the Hubble anomaly. Especially when a kinetic-energy-dominated phase appears after the phase transition, the DE density dilutes faster than radiation and satisfies the requirements for solving the H 0 anomaly. In our scenario, unlike in originally proposed early DE theory, the DE density is controlled by (eV) neutrino mass and it does not require a fine-tuned EDE scale. We perform a Markov Chain Monte Carlo analysis and confront our model with Planck + SHOES and baryon acoustic oscillation data and find evidence for a nonzero neutrino–scalar EDE density during MRE. Our analysis shows that this model is in agreement to nearly 1.3σ with SHOES measurement, which is H 0 = 74.03 ± 1.42 km s−1 Mpc−1.

Mixing and combustion at low heat release in large eddy simulations of a reacting shear layer

In this paper, the mixing and combustion at low-heat release in a turbulent mixing layer are studied numerically using large eddy simulation. The primary aim of this paper is to successfully replicate the flow physics observed in experiments of low-heat release reacting mixing layers, where a duty cycle of hot structures and cool braid regions was observed. The nature of the imposed inflow condition shows a dramatic influence on the mechanisms governing entrainment, and mixing, in the shear layer. An inflow condition perturbed by Gaussian white noise produces a shear layer which entrains fluid through a nibbling mechanism, which has a marching scalar probability density function where the most probable scalar value varies across the layer, and where the mean-temperature rise is substantially over-predicted. A more sophisticated inflow condition produced by a recycling and rescaling method results in a shear layer which entrains fluid through an engulfment mechanism, which has a non-marching scalar probability density function where a preferred scalar concentration is present across the thickness of the layer, and where the mean-temperature rise is predicted to a good degree of accuracy. The latter simulation type replicates all of the flow physics observed in the experiment. Extensive testing of subgrid-scale models, and simple combustion models, shows that the WALE model coupled with the Steady Laminar Flamelet model produces reliable predictions of mixing layer diffusion flames undergoing with fast chemistry.

Symmetry potentials and in-medium nucleon-nucleon cross sections within the Nambu–Jona-Lasinio model in relativistic impulse approximation

In the relativistic impulse approximation (RIA), we study symmetry potentials and in-medium nucleon-nucleon (NN) cross sections with the Nambu-Jona-Lasinio (NJL) model that features chiral symmetry. The chiral symmetry that plays a fundamental role in the nonperturbative physics in the strong interaction is anticipated to add restrictive effects on the symmetry potentials and in-medium NN cross sections. For comparison, we also perform the study with the usual relativistic mean-field (RMF) model. The numerical results with the NJL and RMF models are similar at saturation density and below, since a priori fit was made to saturation properties. With the increase of nuclear density, the chiral symmetry starts to be restored partially in the NJL model, resulting in the explicit fall of the scalar density. In a large energy span, the symmetry potential acquires a significant rise for the partial restoration of the chiral symmetry, compared to the one with the RMF model. It is found that the in-medium NN cross sections in the RIA with the NJL and RMF models both increase with the density in the energy region interested in this study, whereas those with the NJL model increase sharply as long as a clear chiral symmetry restoration takes place. The different tendency of observables in density can be transmitted to the different energy dependence in the RIA. The NJL model is shown to have characteristic energy-dependent symmetry potentials and NN cross sections beyond saturation point, apart from the RMF models.

Estimating the Polytropic Indices of Plasmas with Partial Temperature Tensor Measurements: Application to Solar Wind Protons at ~1 au

We examine the relationships between temperature tensor elements and their connection to the polytropic equation, which describes the relationship between the plasma scalar temperature and density. We investigate the possibility to determine the plasma polytropic index by fitting the fluctuations of temperature either perpendicular or parallel to the magnetic field. Such an application is particularly useful when the full temperature tensor is not available from the observations. We use solar wind proton observations at ~1 au to calculate the correlations between the temperature tensor elements and the scalar temperature. Our analysis also derives the polytropic equation in selected streamlines of solar wind plasma proton observations that exhibit temperature anisotropies related to stream-interaction regions. We compare the polytropic indices derived by fitting fluctuations of the scalar, perpendicular, and parallel temperatures, respectively. We show that the use of the parallel or perpendicular temperature, instead of the scalar temperature, still accurately derives the true, average polytropic index value, but only for a certain level of temperature anisotropy variability within the analyzed streamlines. The use of the perpendicular temperature leads to more accurate calculations, because its correlation with the scalar temperature is less affected by the anisotropy fluctuations.

Change of 0.34Cr-1Ni-Mo-Fe Steel Dislocation Structure in Plasma Electrolyte Hardening.

This work deals with the study of changes in the dislocation structure and quantitative characteristics, as well as morphological components, of 0.34Cr-1Ni-Mo-Fe steel before and after plasma electrolytic hardening. According to the electron microscopic studies of the fine structure of 0.34Cr-1Ni-Mo-Fe steel before and after plasma electrolytic hardening, 0.34Cr-1Ni-Mo-Fe steel is a multiphase material containing an α-phase, a γ-phase (retained austenite), and a cementite and carbide phase. It was revealed that, morphologically, the α-phase in the initial state, generally, is present in the form of: lamellar pearlite with a volume fraction of 35%, a ferritocarbide mixture with a volume fraction of 45%, and fragmented ferrite with a volume fraction of 20% of the material. After surface hardening, the morphological components of the structure changed: packet–lamellar martensite with volume fractions of 60% and 40%, 5% and 7% of γ-phase as residual austenite in the crystals of packet–lamellar martensite, 0.6% and 1.5% of cementite in crystals of packet–lamellar martensite, and 0.15% and 0.35% of complex carbide M23C6 in crystals of packet–lamellar martensite, respectively, were observed. The quantitative characteristics of the dislocation structure were estimated by the following calculated indices of packet and lamellar martensite: scalar (ρ) and excess (ρ±) density of dislocations, the value of the curvature-torsion of the crystal lattice (χ), the amplitude of long-range internal stresses (σd), and the amplitude of shear stresses (σL), according to which the plastic nature of the bending-torsion of the crystal lattice was confirmed (σL > σd).

Physical Nature of Strengthening Mechanisms During Extremely Long-Term Operation of Rails

The quantitative estimation of strengthening mechanisms of rails’ surface layer is carried out on the basis of regularities and formation mechanisms of structure-phase states revealed by the methods of modern physical materials science. It is performed at different depths of the rail head along the central axis and fillet of differentially quenched 100-meter rails after the extremely long-term operation (gross passed tonnage of 1411 mln tons). A long-term operation of rails is accompanied by the formation of structural constituent gradient consisting of a regular change in the relative content of lamellar pearlite, fractured pearlite, the structure of ferrite-carbide mixture, scalar, and excess dislocation density along the cross-section of the rail head. As the distance to the rail fillet surface decreases, the relative content of metal volume with lamellar pearlite decreases. However, the relative content of metal volume with the presence of the fractured pearlite structure and ferrite-carbide mixture increases. The contributions caused by the matrix lattice friction, intraphase boundaries, dislocation substructure, presence of carbide particles, internal stress fields, solid-solution strengthening, pearlite component of steel structure are estimated. It is shown that the main mechanism of strengthening in the surface layer is due to the interaction of moving dislocations with low-angle boundaries of nanometer dimensional fragments and subgrains. The main dislocation strengthening mechanism in a near-surface layer at a depth of 2-10 mm is due to the interaction of moving dislocations with immobile ones.

Experimental simulation of stationary and traveling density-driven thunderstorm downbursts using the two-fluid model

In the present study, novel release mechanisms were developed for laboratory simulations of density-driven downbursts using the two-fluid model. The ability of these new designs in producing repeatable outflows was examined and the influence of minimizing the release cylinder wall effect was tested. The entire experimental setup was also modified to simulate the effect of translation on the resultant downburst wind flows. Planar laser induced fluorescence (PLIF) technique was utilized to visualize the flows and to provide quantitative scalar (density) field data. The results from this study showed a clear difference between the flow fields arising from the two release mechanisms, namely, a higher degree of mixing with ambient fluid, lower downward speed and higher radial propagation rate at the early stages of the simulated downburst lifecycle for the porous wall cylinder. The outflows of stationary and traveling downbursts were compared and the differences between their flow fields and propagation rates were elaborated; for the shear flows tested, a linear relationship between the downburst displacement and storm translation velocity was obtained. The radial outflows of the simulated downbursts were compared to the empirical gravity currents and the mixing of downburst and ambient fluids was quantified using calibrated PLIF images.

Joint-velocity scalar energy probability density function method for large eddy simulations of compressible flow

The combination of large eddy simulation (LES) and probability density function (PDF) methods is a general framework to model turbulent reactive flows. The coupled approach provides direct closures for the nonlinear subgrid source terms typical of chemically reacting flows. LES-PDF methods have a wide range of applicability and they are started to be used in high-speed flows with strong compressibility effects. However, PDF formulations are more complex in compressible flows, where mechanical and thermodynamic contributions are more coupled. The paper presents a novel PDF framework that uses a full thermodynamic closure (scalar-energy-density-velocity) with the Eulerian Monte Carlo stochastic field approach. The work uses simple closures for the subgrid terms using the advantages of the Eulerian formulation and recasts the stochastic equations in a pseudoconservative form. The resultant formulation is applied to three canonical compressible flows: turbulent shock-tubes, compressible homogeneous turbulence, and a reactive free-moving premixed flame. All cases show large density and pressure fluctuations. The effects of underlying numerical schemes and PDF closures to represent compressible effects are investigated along with the statistical convergence of the method.

Growth of accretion driven scalar hair around Kerr black holes

Scalar fields around compact objects are of interest for scalar-tensor theories of gravity and dark matter models consisting of a massive scalar, e.g. axions. We study the behaviour of a scalar field around a Kerr black hole with non trivial asymptotic boundary conditions - both non zero density and non zero angular momentum. Starting from an initial radially homogeneous configuration, a scalar cloud is accreted, which asymptotes to known stationary configurations over time. We study the cloud growth for different parameters including black hole spin, scalar field mass, and the scalar field density and angular momentum far from the black hole. We characterise the transient growth of the mass and angular momentum in the cloud, and the spatial profile of the scalar around the black hole, and relate the results of fully non-linear simulations to an analytic perturbative expansion. We also highlight the potential for these accreted clouds to create monochromatic gravitational wave signals - similar to the signals from superradiant clouds, although significantly weaker in amplitude.

Paradigm of warm quintessential inflation and production of relic gravity waves

We consider the framework of quintessential inflation in the warm background which is caused by the dissipation of the scalar field energy density into relativistic degrees of freedom. The dissipation process has important consequences for the evolution both at the levels of background as well as perturbation and allows us to easily satisfy the observational constraints.~Our numerical analysis confirms that the model conforms to observational constraints even if the field-radiation coupling strength is weak. In the warm background, we investigate the post inflationary evolution of relic gravity waves produced during inflation whose amplitude is constrained by the Big Bang Nucleosynthesis constraint. Further, we investigate the effect of coupling on the amplitude of gravity waves and obtain the allowed phase space between the model parameters. The mechanism of quintessential inflation gives rise to the blue spectrum of gravitational wave background at high frequencies. We discuss the perspectives of detection of the signal of relic gravity waves by future proposed missions. Improvements of their sensitivities in the high-frequency regime, in the future, might allow us to probe the blue tilt of the spectrum caused by the presence of a kinetic regime in the underlying framework of inflation.

The continuous eddy simulation capability of velocity and scalar probability density function equations for turbulent flows

There is a well developed spectrum of computational methods for turbulent flows: modeling methods such as Reynolds-averaged Navier–Stokes (RANS) and probability density function (PDF) methods, and resolving methods such as large eddy simulation (LES) and filtered density function (FDF) methods. However, the applicability of RANS/PDF methods is limited to flows that do not essentially require the inclusion of resolved motion, and LES/FDF methods are well applicable if resolution criteria can be satisfied [which is often infeasible for very high Reynolds number (Re) wall-bounded turbulent flows]. A highly attractive approach to overcome these problems is the design of hybrid RANS–LES methods, which can be used with varying amounts of resolved and modeled motions. However, this approach faces the problem to ensure communication and balancing of resolved and modeled motions. A well working solution to this problem was presented recently for non-homogeneous flows with respect to velocity two-equation eddy viscosity turbulence models. Exact analytical results regarding the extension of these methods to velocity and passive scalar PDF/FDF methods and their implied RANS/LES equations are presented here. The latter matters with respect to the justification of the theoretical basis of new hybrid methods (realizability) and the availability of a hierarchy of simple and advanced simulation methods (including passive scalar transport). Based on the continuous mode redistribution mechanism, the new simulation methods are capable of providing reliable predictions of very high Re turbulent flows, which cannot be accomplished by using existing techniques.

Impact of Electronic Radiation on the Morphology of the Fine Structure of the Surface Layer of R6M5 Steel

In recent decades, great efforts have been made to significantly improve the performance characteristics of high-speed steel using various surface hardening techniques. Electron beam modification is engaging because it has an exceptionally high thermal efficiency and can significantly improve steels’ physical and mechanical properties. This work is devoted to researching the fine structure and changing the structural phase state of the surface layer of R6M5 high-speed steel after exposure to an electron beam. Electron beam treatment of steel R6M5 was carried out on a vacuum installation. The structure and phase composition of P6M5 steel samples were studied by transmission electron microscopy. Determined that after electron irradiation, the steel structure as in the initial state consists of martensite, carbides and residual austenite. After electron irradiation, an increase in the volume fraction of lamellar martensite is observed: the fraction of lamellar martensite in the initial state is 80%, and after irradiation, it is ~90% of the total fraction of α′-martensite. The action of the electron beam led to an increase in internal stresses in α′-martensite. Revealed, the value of the scalar dislocation density in R6M5 steel after exposure to an electron beam is higher than in the initial state. A cardinal difference in the state of the material after exposure to an electron beam is the presence of bending extinction contours in all M6C carbide particles.

Numerical Prediction of Turbulent Spray Flame Characteristics Using the Filtered Eulerian Stochastic Field Approach Coupled to Tabulated Chemistry

The Eulerian stochastic fields (ESF) method, which is based on the transport equation of the joint subgrid scalar probability density function, is applied to Large Eddy Simulation of a turbulent dilute spray flame. The approach is coupled with a tabulated chemistry approach to represent the subgrid turbulence–chemistry interaction. Following a two-way coupled Eulerian–Lagrangian procedure, the spray is treated as a multitude of computational parcels described in a Lagrangian manner, each representing a heap of real spray droplets. The present contribution has two objectives: First, the predictive capabilities of the modeling framework are evaluated by comparing simulation results using 8, 16, and 32 stochastic fields with available experimental data. At the same time, the results are compared to previous studies, where the artificially thickened flame (ATF) model was applied to the investigated configuration. The results suggest that the ESF method can reproduce the experimental measurements reasonably well. Comparisons with the ATF approach indicate that the ESF results better describe the flame entrainment into the cold spray core of the flame. Secondly, the dynamics of the subgrid scalar contributions are investigated and the reconstructed probability density distributions are compared to common presumed shapes qualitatively and quantitatively in the context of spray combustion. It is demonstrated that the ESF method can be a valuable tool to evaluate approaches relying on a pre-integration of the thermochemical lookup-table.

Scalar fluctuation and its dissipation in turbulent reacting flows

The dissipation rate of a scalar variance is related to the mean heat release rate in turbulent combustion. Mixture fraction is the scalar of interest for non-premixed combustion, and a reaction progress variable is relevant for premixed combustion. A great deal of work is conducted in past studies to understand the spectra of passive scalar transport in turbulent flows. A very brief summary of these studies to bring out the salient characteristics of the passive scalar spectrum is given first. Then, the classical analysis of the reactive scalar spectrum is revisited in the lights of recent understanding gained through analyzing the scalar spectrum deduced from direct numerical simulation data of both non-premixed and premixed combustion. The analysis shows that the reactive scalar spectral density in premixed combustion has a dependence on Karlovitz and Damköhler numbers, which comes through the mean scalar dissipation rate appearing in the spectral expression. In premixed combustion, the relevant scale for the scalar dissipation rate is shown to be of the order of the chemical length scale, and the dissipation rate is not influenced by the scales in the inertial-convective range unlike for the passive scalar dissipation rate. The scalar fluctuations produced near the chemical scales cascade exponentially to larger scales. These observations imply that the passive scalar models cannot be extended to premixed combustion.

Studying the Surface Layer Structure of 40Cr Steel after Rough and Semi-Finished Machining

The results of studies of the microstructure and local fields of internal stresses arising in the surface layer of 40Cr steel samples processed in two modes: rough and semi-finished (chip removal to a depth of 1.0 and 0.5 mm, respectively) are presented. The internal structure of all morphological steel components is investigated. The scalar dislocation density and the width of the bending extinction contours are measured and calculated, from which the amplitude of the curvature torsion of the crystal lattice of the forming phases, the excess dislocation density, and the amplitude of internal stresses in different sections of the material are determined. In the initial state, the 40Cr steel matrix is α phase, a solid solution of carbon and alloying elements in α-Fe with a body-centered cubic (bcc) lattice. The morphological components of the α phase are lamellar perlite and ferrite. Rough machining leads to the formation of secondary fragmented perlite. After semi-finishing, lamellar perlite is formed with curved cementite plates.

Структура и свойства поверхностного слоя цирконий-ниобиевого сплава, подвергнутого высокодозной имплантации ионами изотопа бора 10В+

The creation of layers implanted with boron isotope 10B on the elements of the core of a nuclear reactor can, due to the anomalously large neutron capture cross-section, provide a decrease in the reactivity of the reactor at the beginning of the company for its operation. The aim of this work is to study the effect of high-dose implantation with 10B + boron isotope ions (ion energy 22 keV, exposure doses from 1×1016 to 7×1016 ion/cm2) on the structure and properties of the surface of E110 alloy samples. It was found that implantation with 10B+ boron ions with an energy of 22 keV at a dose of 7×1016 ions/cm2 leads to an increase in the surface microhardness from 3 GPa for the initial one to 3.7 GPa for the implanted sample. It was found that the corrosion rate of E110 alloy samples in 1% HF solution after implantation (ion energy 10B + 22 keV, dose 7×1016 ion/cm2) is 1.2-1.4 times lower than for the initial alloy. It is shown that the implantation of the E110 alloy with 10B + boron ions is accompanied by the formation of a subgrain structure with dimensions 100-200 nm in the surface layer, an increase in the scalar dislocation density, and the release of nanosized 1.8-2.3 nm zirconium boride particles.

Эволюция микроструктуры и ее параметров с деформацией в поликристаллических сплавах медь - алюминий с разной энергией дефекта упаковки

Evolution of the dislocation structure during active plastic deformation was carried out in copper-aluminum alloys with Al content of 0.5-14 at. % using transmission electron microscopy. Analysis of the types of the dislocation substructure as a function of the alloying element content and deformation degree was conducted. The following parameters of the defect substructure were measured: average scalar dislocation density, curvature-torsion of the crystal lattice and microtwin density. The effect of stacking fault energy on accumulation of defects in the alloys was observed and evaluated.

Структурно-фазовые состояния и свойства поверхности катания рельсов при экстремально длительной эксплуатации

Using the methods of modern physical material science the investigations of structure-phase states and properties at different depth from tread surface of differentially quenched rails at extremely long-term operation (passed tonnage 1411 mln t) are carried out. The hardness decrease from 37.1 to 35.8 HRC at the depth 2 and 10 mm and microhardness from 1481 to 1210 MPa, respectively is revealed. The established multiple transformation of tread surface structure concludes in: fracture of lamellar pearlite structure and subgrain structure formation of submicronsizes (100-150 nm); precipitation of carbide phase nanoparticles (30-55 nm)along the boundaries and in the volume ofsubgrains; growth of microdistorsions and α-Fe crystal lattice parameter; growth of scalar and excess dislocation density. The suggestions about the possible reasons of observable regularities are made.