Warm dense matter (WDM) is a state of a substance with a solid-state density and temperature from 1 to 100 eV. Researchers believe that such a state exists in the cores of giant planets. Investigation of WDM is important for some applications, such as surface treatment on the nanometer scale, laser ablation, and the formation of the plasma sources of the X-ray radiation into the inertial synthesis. In this study, the conductivity and the thermal conductivity are calculated based on density functional theory and the Kubo-Greenwood theory. This approach was already used to simulate the transport properties in a broad range of densities and temperatures, and its efficiency has been demonstrated. The conductivity and the thermal conductivity of aluminum and gold are investigated. Both the isothermal state, when the electron temperature equals the ion temperature, and the two-temperature state, when the electron temperature exceeds the ion temperature, are considered. The calculations were performed for a solid body and liquid in the range of electron temperatures from 0 to 6 eV.
A method for computing the components of the Euler–Poinsot tensors up to the fourth order in the expansion of the gravitational potential is described. The results are illustrated by the example of asteroid 433 Eros.
—The structural transformation of solid hydrogen under compression along the isotherm of 100 K in the region of transition into the conductive state was studied within the density functional theory. The pressure, the pair correlation function of protons, the density of electron states, and the electrical conductivity were calculated within a range of hydrogen densities from 1.14 to 2.11 g/cm3. The transition of the monoclinic structure of molecular solid hydrogen into the orthorhombic Cmca structure with 12 hydrogen atoms in a unit cell was revealed. In this case, the electrical conductivity was observed to grow, though hydrogen remained molecular. Hydrogen molecules decomposed under compression to the density of 1.563 g/cm3. A unit cell, the thus-formed quasi-tetrahedron, was built of five protons with a distance of 0.92 Å from the central proton to the four others.
An approach to the estimation of the initial shape of a meteoroid based on the statistical distributions of masses of its recovered fragments is presented. The fragment distribution function is used to determine the corresponding scaling index of the power law with exponential cutoff. The scaling index is related empirically to the shape parameter of a fragmenting body by a quadratic equation, and the shape parameter is expressed through the proportions of the initial object. This technique is used to study a representative set of fragments of the Bassikounou meteorite and compare the obtained data with the results of statistical analysis of other meteorites.
The nonlinear dynamics of multisoliton, differently polar fields is investigated within the framework of the modified Korteweg–de Vries equation. It is shown that the occurrence of abnormally large waves (freak waves) is possible in similar fields, which is associated with the modulation instability of cnoidal waves. The statistical moments of wave fields are investigated. It is shown that an increase in the coefficient of excess due to the interaction of solitons correlates with an increase in the probability of occurrence of freak waves. It is shown that the nonlinear interaction of differently polar solitons results in variation of the distribution functions of peak characteristics: the fraction of low-amplitude waves decreases, while that of the waves with large amplitudes increases. The dependence of the intensity of the density of the characteristics of the soliton gas is shown.
The problem of the free motion of two bodies connected by a pair of spherical hinges is considered.The conditions for the existence of invariant relations analogous to the Hess integral are specified.
Warm dense hydrogen is investigated by the ab initio molecular dynamics method near the fluid– fluid phase transition. The metastable states are calculated along isotherms of 700 and 1000 K. The obtained pressure ranges of metastable states are 0.47 and 0.32 Mbar, respectively. Their existence indicates that this transition is a first-order phase transition.
The motion of a massive point (a bead) over the surface of a uniformly rotating asteroid is considered. It is assumed that the force of dry friction acts between the point and the asteroid surface. The sets of nonisolated positions of relative equilibrium of the bead on the asteroid are described, and their dependence on the parameters of the problem is investigated. The results are presented as bifurcation diagrams.
The temperature dependence of the conductivity of the topological Kondo-insulator (TKI) Sm1 – xYbxB6 is investigated in the temperature range 2 < T < 300 K for compositions with x ≤ 0.024. It is found that the ytterbium impurity most strongly affects the low-temperature (T < 20 K) electrical conductivity: when changing from x = 0 to x = 0.024, the activation energy of bulk conductivity decreases by 1.8 times from 4 to 2.2 meV, and the 2D surface conductivity increases by six times. The separation made for the contributions to the conductivity enables us to establish that the one-parameter scaling model can be used for describing the conductivity of 2D surface states in the Sm1 – xYbxB6 TKI in which both the interaction with phonons and the electron–electron scattering effects are taken into account.
The change in the structure of solid hydrogen upon compression along the isotherm of 100 K near the transition to the conducting state has been investigated within the density-functional theory. The dependences of pressure and electrical conductivity on the hydrogen density have been calculated. The pressure range from 602 to 836 GPa has been found where the first peak of the pair correlation function arises at a distance of 0.92 Å, which corresponds to the interatomic distance in the molecular H3+ ion. Notably, this distance does not change with an increase in density. A sharp increase in the electrical conductivity is also observed.
The problem of the fluid–fluid phase transition in warm dense hydrogen/deuterium has been studied experimentally and theoretically in the best laboratories in the last decade. However, the nature of the phase transition remains unclarified. In this paper we put forward the new idea that H2 molecules are ionized at the phase transition to produce molecular Н2+ and Н3+ ions
Quantum size phenomena develop when the dimension(s) of a system approach certain characteristic scales. Modern nanotechnology enables routine and reproducible fabrication of nanostructures with sub-100 nm features where such effects might be pronounced. In this research we used lift-off lithography and vacuum metal deposition to fabricate bismuth (semimetal) and titanium (superconductor) nanowires. Then low energy argon ion beam etching was used to progressively reduce the cross section of the structures. Electron transport properties were measured at low temperatures between the sessions of etching. Oscillations of electric resistance and its pronounced increase below ~70 nm scales were observed when bismuth nanowire cross section was reduced. The observation can be interpreted as a manifestation of electron spectra size quantization in narrow semimetal channels. We observed broadening of the resistive transition in superconductors with reduction of the nanowire cross section. In the thinnest samples finite resistance was observed even at temperatures much lower than the bulk critical temperature. The phenomenon can be understood as manifestation of the quantum phase slip effect specific for ultra narrow superconducting channels. Both quantum size effects (in semimetals and superconductors) are in good agreement with the existing models. The existence of quantum size phenomena in metallic systems imposes fundamental limitations on the utilization of such ultra-small components in nanoelectronic circuits.
The density functional theory is used to calculate the equation of state and the proton-proton pair correlation functions in the range of hydrogen temperatures and densities where the fluid-fluid-phase transition is expected. The metastable states are considered. The critical temperature has been estimated to be ~4000 K. We propose a two-step mechanism: the partial ionization of molecules to produce ions H2+ at the phase transition followed by the formation of ions H3+.