Shock waves actions upon materials perspective for using in future thermonuclear fusion reactors are investigated experimentally and by means of numerical modelling. The shocks are generated by powerful streams of plasma and fast ions in Dense Plasma Focus devices as well as by irradiation with a laser operating in a Q-spoiled mode. Power flux densities of these streams on the targets’ surfaces are in the range 1014 – 1016 W/m2. They are used for tests of the above materials, and their influences are compared for a number of substances. It is shown that in the above-mentioned identical conditions Plasma Foci generate shock waves with amplitudes of approximately two times higher than that for the laser case. Fronts of the shocks are formed here faster than at the laser irradiation. A simple analytical formula for calculations of the amplitudes of shock waves in radiation material science experiments provided with Dense Plasma Focus devices are advanced.
Residual stresses arising in the drawing process have a significant impact on the quality of the cold-drawn wire. Knowledge of residual stresses and their distribution makes it possible to predict the behavior of metal products under operating loads and to prevent their possible destruction. In this regard, it is necessary to adjust the main parameters of the drawing process, including the geometry of the die channel. The work is devoted to the study of residual stresses arising from inhomogeneity of plastic deformation depending on the reduction value and the die angle. Computer simulation of wire drawing process by finite element method is performed. The distributions of residual stress tensor components along the wire radius are calculated for different values of reduction and die angle. The analysis of the obtained relations is carried out. The influence of the die angle on the distribution of residual stresses is most noticeable at small reductions. After the maximum values of residual stresses are reached at the reduction values of 35-40%, they noticeable decrease occurs.
The article examines the recent ‘schism’ in Eastern Orthodoxy to show how religion and politics are strongly intertwined in disputes over territory and sovereignty. It argues that two logics are at play in this conflict: one grounded in the theological‐political concept of ‘canonical territory’, the other in the notion of ‘communion’ at the basis of the Christian fellowship. The first is deployed in claims for national sovereignty as well as imperial domination, while the latter can make or break communities of faith. Drawing a parallel between the post‐socialist revival of religion in Ukraine and the current mobilization on the ground, it shows how these contradictory logics shape the fate of people, churches and states.
We show that the terahertz (THz) photoconductivity in the topological phase of Hg1–xCdxTe-based structures exhibits the apparent PT- (parity-time) symmetry whereas the P-symmetry and the T-symmetry, separately, are not conserved. Moreover, it is demonstrated that the P- and T-symmetry breaking may not be related to any type of the sample anisotropy. This result contradicts the apparent symmetry arguments and means that there exists an external factor that interacts with the sample electronic system and breaks the symmetry. We show that deviations from the ideal experimental geometry may not be such a factor.
We report on the quantum yield (eta) and decay time (tau) measurements at room temperature for the bright red-orange (602 nm) luminescence from new germanium-vacancy (Ge-V) centers in nano- and microcrystalline diamonds synthesized at high pressure and high temperature. The values eta = 3 +/- 1% and tau = 6.2 +/- 0.2 ns were found. The Stokes shift measured as the energy difference between the maxima of the luminescence and luminescence excitation spectra is negligible. The relative intensity of the zero-phonon line constitutes up to 70% from the total intensity of the luminescence. Results of our ab initio DFT calculations for the ground-state electronic and vibrational structure of (Ge-V)(-) in diamond are presented and discussed.
For the past five years methyl-ammonium lead trihalide perovskite solar cells have shown remarkable progress in power conversion efficiencies due to their unique properties. Single CH3NH3PbI3 crystals were grown on the base of concentrated aqueous solution condensation of the precursor. The grown crystal structure and stoichiometry were studied by RHEED, X-ray and XPS. The perovskite crystal photocurrent spectra were measured in the temperature range of 85-330 K.
The work is dedicated to determination of stress-strain behavior of Ti6Al4V alloy deformed in conditions of biaxial tension provided by free bulging testing. The dome height during each test was continuously measured and recorded using a magnetostrictive position transducer. All the tests were performed using stepped pressure regime with jump pressure changing between two values at evenly spaced time moments. This experimental technique provides the possibility to study strain rate sensitivity index variation during the test and subsequently construct strain and strain rate dependent material model. The output data of each test include the evolution of dome height, subsequent pressure regime and final thickness of the specimen at the dome pole. In the framework of this study the processing of such data in order to evaluate the material behavior is discussed. Inverse analysis with different material models was implemented as well as special direct technique allowing one to construct stress-strain curves based on the results of free bulging tests with pressure jumps. The obtained material model was verified by finite element simulation.
We report an observation of coherent phonons of E-g(1), E-u(1), A(1g)(1), and E-g(2) symmetry generated in a single-crystal film of Bi2Se3 by an intense single-cycle THz pulse. The atomic vibrations reveal themselves through periodic modulation of the refractive index of the film. The largest signal is detected at the frequency of 4.05 THz that corresponds to the E-g(2) mode. The generation of E-g(2) phonons is interpreted as resonant excitation of the Raman mode by the second harmonic of THz-driven nonlinear E-u(1) oscillator, the fundamental frequency of which (2.05 THz) is approximately half that of E-g(2). The origin of nonlinearity in this case is cubic lattice anharmonicity, while generation of E-g(1) (1.1 THz) and A(1g)(1) (2.25 THz) phonons is a manifestation of quartic anharmonicity enhanced by the occasional combination relations between phonon frequencies in Bi2Se3.
The kinetics of the electronic transitions within the f -shell of Dy3+ ions were studied with monitoring near- and mid-IR luminescence decay under pulsed laser excitation at 1.3 μm. The luminescence decay curves were found to be profoundly non-exponential in all bands in the range between 1.3-5.5 μm. Such behavior is attributed to cross-relaxation and up-conversion processes dominating in relaxation of Dy3+ ions from the laser-excited multiplet 6H9-2+6F11-2. We suggest that strong collective phenomena occurring under relatively low concentrations are due to anomalous clustering of Dy3+ ions. The cross-relaxation enables an efficient population of 6H13-2 and 6H11-2 multiplets, offering this material as an active medium for a 3-μm and 4.3-μm lasers.
The article shows an influence of kind of tests on material hot defamation behaviour during physical modelling on Gleeble 3800. As material, high-strength low-alloy automobile steel HC420LA was used. Stress-strain curves and material constants based on results of flow stress and plain strain tests were calculated and compared. Besides finite-element modeling of rolling round bar on a smooth barrel was performed taking into account the calculated mechanical characteristics.
The intercalation of H2O, CO2, and other fluid species in expandable clay minerals (smectites) may play a significant role in controlling the behavior of these species in geological C-sequestration and enhanced petroleum production and has been the subject of intensive study in recent years. This paper reports the results of a computational study of the effects of the properties of the charge balancing, exchangeable cations on H2O and CO2 intercalation in the smectite mineral, hectorite, in equilibrium with an H2O-saturated supercritical CO2 fluid under reservoir conditions using Grand Canonical Molecular Dynamics (GCMD) methods. The results show that the intercalation behavior is greatly different with cations with relatively low hydration energies and high affinities for CO2 (here Cs+) than with cations with higher hydration energies (here Ca2+). With Cs+, CO2 intercalation occurs in a 1-layer structure and does not require H2O intercalation, whereas with Ca2+ the presence of a sub-monolayer of H2O is required for CO2 intercalation. The computational results provide detailed structural, dynamical and energetic insight into the differences in intercalation behavior and are in excellent agreement with in situ experimental XRD, IR, quartz crystal microbalance, and NMR results for smectite materials obtained under reservoir conditions.
The solidification of liquid copper in a porous refractory tungsten skeleton subjected to infiltration and subsequent cooling under various conditions, including a standard through-type furnace cooler, is studied. The pores in the refractory skeleton are shown to be completely filled with liquid copper in the presence of excess melt up to the end of infiltration. Heat insulation is found to be a practical method to retain excess liquid copper up to its solidification inside the porous refractory skeleton. Standard Termoizol-1400 is used as a heat insulator. At a heat insulator wall thickness of 10.8 mm, the excess liquid copper layer thickness is 0.2 mm up to the end of infiltration of a W–Cu pseudoalloy. Criteria are proposed for rational infiltration.
The FeSe wires and tapes with Fe (S22 steel) and Cu/Nb sheath were fabricated by various modifications of the powder-in-tube (PIT) method. The superconducting critical parameters (upper critical field, critical current, critical temperature) depending on heat treatment time were investigated using resistive R(T) and transport measurements I (V) in magnetic fields up to 9T. The low-temperature annealing up to 72 h improve superconducting properties of superconducting wire with steel sheath. However, the annealing is the cause of superconducting wires degradation due to deterioration of contacts between the steel shell and the FeSe core. We show that industrial PIT technology of manufacturing Nb3Sn wires and tapes might be adopted for iron-based superconductors. Moreover, industrial PIT is a promising technique for fabricating large scale and high-quality superconducting wire and tapes. In addition, we show that fine grinding of the FeSe bulks leads mainly to a phase transition from the tetragonal to the hexagonal crystal structure that exhibits no superconductivity.
In “Lattice dynamics and structure of the new langasites Ln3CrGe3Be2O14 (Ln ¼ La, Pr, Nd): vibrational spectra and ab initio calculations” , experimental and calculated results on lattice dynamics of the recently discovered new compounds La3CrGe3- Be2O14, Pr3CrGe3Be2O14, and Nd3CrGe3Be2O14 are reported. These compounds belong to the langasite series and constitute a new class of low-dimensional antiferromagnets. The data presented in this article includes IR diffuse transmission spectra of powder samples of Ln3CrGe3Be2O14 (Ln ¼ La, Pr, Nd) registered at room temperature with a Bruker 125HR Fourier spectrometer, Raman spectra taken in the backscattering geometry (also at room temperature) with a triple monochromator using the line 514, 5 nm of an argon laser as an excitation, results of the DFT calculations with the B3LYP and PBE0 hybrid functionals on the optimized crystal structures, eigenfrequencies and eigenvectors of the normal vibrational modes. These data can be used to analyse electronphonon interaction and multiferroic properties of the new langasites and to compare the lattice dynamics of different langasites.
Adsorption of fluids in nanoporous media causes mechanical stresses which results in deformation. This phenomenon is ubiquitous and its magnitude depends on the pore size and geometry. Adsorption and adsorption-induced deformation are typically modeled in slit-shape or convex (cylindrical or spherical) pores. However, many porous materials are composed of spherical grains, so that the pores are formed by the intergranular spaces between the convex solid surfaces. Here we present a first theoretical study of adsorption-induced deformation in non-convex pores, in particular we studied the templated mesoporous carbons. The model is based on classical density functional theory within the local density approximation applied to the description of hard sphere interactions. We predict the adsorption isotherms and solvation pressure isotherms for nitrogen adsorption in CMK-3 carbons. The shape of adsorption isotherm matches the shape of experimental isotherm. The predicted solvation pressure isotherms are qualitatively different from the solvation pressure isotherms in cylindrical pores. We attribute this difference to formation of liquid bridges between the adjacent rods. Our results suggest that adsorption-induced deformation in materials with non-convex pores cannot be predicted within the existing models. These results may shed some light on understanding adsorption-induced deformation of consolidated granular media.
The structural and spectroscopic features of the EuAl3(BO3)4 individual skeletal microcrystals synthesized by a melt solution method have been studied. Their infrared spectra taken from the as-grown microcrystal surfaces mainly contain the lines of the rhombohedral modification of EuAl3(BO3)4 and additional peaks of its monoclinic modification. TEM and X-ray diffraction studies confirm that these additional peaks in the IR spectra belong to the monoclinic C2/c polytype of the EuAl3(BO3)4 compound. We are the first to demonstrate the presence of coherent monoclinic domains in rhombohedral EuAl3(BO3)4 crystals by TEM. Cathodoluminance spectroscopy shows that the microcrystals generate strong emission lines in the range 580–630 nm, and their intensities are strongly influenced by the crystal orientation.
We construct a distribution function of the strain-tensor components induced by point defects in an elastically anisotropic continuum, which can be used to account quantitatively for many effects observed in different branches of condensed matter physics. Parameters of the derived six-dimensional generalized Lorentz distribution are expressed through the integrals computed over the array of strains. The distribution functions for the cubic diamond and elpasolite crystals and tetragonal crystals with the zircon and scheelite structures are presented. Our theoretical approach is supported by a successful modeling of specific line shapes of singlet-doublet transitions of the Tm3+ ions doped into ABO4 (A=Y, Lu; B=P, V) crystals with zircon structure, observed in high-resolution optical spectra. The values of the defect strengths of impurity Tm3+ ions in the oxygen surroundings, obtained as a result of this modeling, can be used in future studies of random strains in different rare-earth oxides.
The structure–phase changes that are caused in the surface layers of ferritic–martensitic Eurofer 97 and 10Cr9WV steel samples by the action of pulsed powerful fluxes of deuterium plasma and deuterium ions, which are generated in a plasma focus (PF) setup, are studied. Before tests, the steels were subjected to standard heat treatment (normalizing, tempering), and the 10Cr9WV steel samples were additionally annealed at 600°C for 600 h to determine the stability of the structure and properties at the temperatures that are close to the operating temperatures. During irradiation, the power densities of plasma (qpl = 107–1010 W/cm2) and ion (qi = 109–1012 W/cm2) fluxes and the number of plasma beam pulses (5–12 at a pulse duration of ~100 ns) are varied. The irradiation of the Eurofer 97 steel at qpl = 108–1010 W/cm2 in the PF setup is shown to cause melting and ultrafast solidification of the surface layer with the subsequent formation of a fine cellular structure with a cell size of 100–150 nm in it. The surface film formed on the 10Cr9WV steel samples during preliminary long-term annealing is found to begin to fail at qpl = 108 W/cm2; this film is fully removed at qpl = 1010 W/cm2. This process is accompanied by the segregation of particles 1–3 μm in size, which are enriched in manganese, chromium, and oxygen. After the surface film is removed, irradiation promotes the removal of manganese from the surface layers, and manganese is also removed from the Eurofer 97 steel, which has no surface film in the initial state. The plasma beam treatment of the Eurofer 97 steel in the PF working chamber at qpl = 108 W/cm2 is found to cause the formation of retained austenite in its structure, and the content of retained austenite in the 10Cr9WV steel subjected to similar treatment is lower than in the Eurofer 97 steel by a factor of 20 because of the presence of a film on its surface. The irradiation of the 10Cr9WV steel at a higher power density (qpl = 1010 W/cm2), when the surface film is removed, equalizes the contents of retained austenite in the steels under study.
We report a comprehensive study of physical properties of the binary superconductor compound SnAs. The electronic band structure of SnAs was investigated using both angle-resolved photoemission spectroscopy (ARPES) in a wide binding energy range and density functional theory (DFT) within generalized gradient approximation (GGA). The DFT/GGA calculations were done including spin-orbit coupling for both bulk and (111) slab crystal structures. Comparison of the DFT/GGA band dispersions with ARPES data shows that (111) slab much better describes ARPES data than just bulk bands. Superconducting properties of SnAs were studied experimentally by specific heat, magnetic susceptibility, magnetotransport measurements and Andreev reflection spectroscopy. Temperature dependences of the superconducting gap and of the specific heat were found to be well consistent with those expected for the single band BCS superconductors with an isotropic s-wave order parameter. Despite spin-orbit coupling is present in SnAs, our data shows no signatures of a potential unconventional superconductivity, and the characteristic BCS ratio 2/Tc = 3.48 − 3.73 is very close to the BCS value in the weak coupling limit.