Contribution to the thermodynamics of the isomorphous γ ⇆ α-transition in metallic cerium

Using the method of the theory of thermodynamic stability and the form of the lines of the phase equilibrium of the isomorphous -transition in metallic cerium, the authors investigate the behavior of the basic thermodynamic characteristics of this transition in the two-phase region and in a neighborhood of the critical point. Attention is focused primarily on the little-studied adiabatic quantities (T/C_V, (–P/V)_S, (T/V)_S). It is shown that along the phase tie-lines these quantities do not depend on V and S; in the limit of the critical point all adiabatic quantities have nonzero minima, and all isodynamic quantities (T/Cp, (–P/V)_T, (T/V)_P) approach zero according to the same law. The obtained thermodynamic results are compared with existing experimental data and models which can be interpreted thermodynamically. It is concluded that critical phenomena in cerium correspond to critical behavior of the first type.Dnepropetrovsk State University Dedicated to the 300th Anniversary of the Unification of the Ukraine with Russia.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 66–70, May, 1991.     

Structure of the α-phase of solid methanol

The crystal structure of α-methanol at 15K has been determined from neutron powder diffraction measurements. The structure is orthorhombic, space group P2₁2₁2₁. The molecular geometry is found to be very similar to that in the gas phase, but the methyl group no longer has ideal 3-fold symmetry. The crystal is formed by infinite hydrogen-bonded chains of molecules with adjacent chains ‘pointing’ in opposite directions. The O-H … O hydrogen bonds are almost linear. No phase intermediate between the low temperature α-phase and the high temperature β-phase was found, but a new, metastable phase was discovered.     

Superconductivity in the metallic–oxidized sodium interface

Superconductivity at 20–34 K in the interface formed by metallic and oxidized sodium has been observed by ac magnetic susceptibility measurements. By means of X-ray diffraction measurements, it has been found that the oxidized sodium layer consists of a mixture of Na₂O, Na₂O₂, NaO₂ and NaO₃ compounds.     

Superconductivity in the metallic–oxidized copper interface

A strong indication of superconductivity at 20–90 K in the interface formed by metallic and oxidized copper has been revealed by ac magnetic susceptibility measurements. By means of X-ray diffraction measurements, it has been found that the oxidized copper consists of a mixture of Cu₂O and CuO compounds.     

Superconductivity in the metallic–oxidized magnesium interface

Metastable superconductivity at 39–54 K in the interfaces formed by metallic and oxidized magnesium (MgO) has been observed by ac magnetic susceptibility measurements. The superconducting interfaces have been produced by the surface oxidation of metallic magnesium under special conditions.     

Energy loss and range of α-particles in different metallic foils

ABSTRACT

The energy loss and range of 5.486?MeV α-particles in Tb, Ta and Au metallic foils is measured, through transmission technique. These measured values are compared with the corresponding computed values adopting commonly used theoretical/semi-empirical formulations (Grande and Schiwietz (CasP 5.2 code), Northcliffe and Schilling, Benton and Henke, ICRU-49 report (ASTAR code) and Ziegler et al. (SRIM-2013.00 code)), with the intention to check the accuracy of the considered formulations.     

Study of slow molecular motions in α-Crystallin by proton magnetic spin-lattice relaxation in the doubly rotating frame

Proton magnetic spin-lattice relaxation in the effective field H₂ acting in the doubly rotating frame (DRF) was first applied to the study of slow internal protein dynamics in the submillisecond range of correlation times in the solid state. In this method the local dipolar magnetic field is reduced by the magic-angle rotating-frame method so that the resonance frequency of the relaxation experiment may be set below the value of the local field. As a result, unachievable by the standard nuclear magnetic resonance (NMR) relaxation techniques, slow molecular motions become experimentally accessible. The second effective field H₂ is produced by the shallow sine-wave phase modulation of the H₁ pulse. The registration of the DRF spin-lattice relaxation signal takes place directly during the continuous H₁ pulse by means of an additional low-frequency radio-frequency coil oriented along the H₀ field and operating at the rotating-frame NMR frequency of 100 kHz. The measurements of the spin-lattice relaxation time in the DRF within a wide temperature range have been performed in dry and hydrated α-crystallin powders. This is the major protein in the eye lens, which prevents the uncontrolled aggregation of proteins and keeps the lens transparent. The results demonstrate that the protein hydration does not change the amplitude of slow side-chain motions but significantly shortens its correlation time: from about 50 to about 0.5 μs in dry and hydrated samples, respectively. The hydration also decreases the activation energy and restricts the distribution of the correlation times.     

24 electron cluster formulas as the ‘molecular’ units of ideal metallic glasses

It is known that ideal metallic glasses fully complying with the Hume-Rothery stabilization mechanism can be expressed by a universal cluster formula of the form [cluster](glue atom)_{1 or 3}. In the present work, it is shown, after a re-examination of the cluster-resonance model, that the number of electrons per unit cluster formula, e/u, is universally 24. The cluster formulas are then the atomic as well as the electronic structural units, mimicking the ‘molecular’ formulas for chemical substances. The origin of different electron number per atom ratios e/a is related to the total number of atoms Z in unit cluster formula, e/a?=?24/Z. The 24 electron formulas are well confirmed in typical binary and ternary bulk metallic glasses.     

Measurement of muon transfer rate λpt and molecular formation rate λppµ, in solid hydrogen targets,in solid hydrogen targets

The knowledge of muon transfer from protium to tritium is essentially theoretical and the different theoretical values disagree partially. Using solid hydrogen-tritium targets, with different tritium concentrations, we obtained precise experimental results for the transfer rate to tritium and the ppµ molecular formation rate. The time spectra of neutrons and alpha particles produced after dtµ fusion are used to determine the transfer rate _pt and the molecule formation rate _ppµ.     

Unconventional anomalous hall effect in the metallic triangular-lattice magnet PdCrO₂

We experimentally reveal an unconventional anomalous Hall effect (UAHE) in a quasi-two-dimensional triangular-lattice antiferromagnet PdCrO?. Using high quality single crystals of PdCrO?, we found that the Hall resistivity ρ(xy) deviates from the conventional behavior below T*?20 K, noticeably lower than T(N)=37.5 K, at which Cr3+ (S=3/2) spins order in a 120° structure. In view of the theoretical expectation that the spin chirality cancels out in the simplest 120° spin structure, we discuss required conditions for the emergence of UAHE within Berry-phase mechanisms.     

Quantum-size effects in the electronic structure of low-dimensional metallic systems

By angle-resolved photoemission the electronic structure of quantum films of Mg, Ag, and Au has been compared on W(110) and Mo(110) substrates which are structurally and electronically very similar but differ in atomic number. In all cases, substrate-induced states with characteristic dispersions are observed in the region of a bulk band gap of the substrate. Based on the comparison between Mo and W, we can exclude that previously observed Mg states are spin-orbit split but observe a spin-orbit splitting in Ag and Au monolayers. This splitting is mainly caused by the substrate because it does not differ much between Ag and Au overlayers despite the large difference in atomic number.     

Tuning the plasmon resonance of metallic tin nanocrystals in Si-based materials

The optical properties of metallic tin nanoparticles embedded in silicon-based host materials were studied. Thin films containing the nanoparticles were produced using RF magnetron sputtering followed by ex situ heat treatment. Transmission electron microscopy was used to determine the nanoparticle shape and size distribution; spherical, metallic tin nanoparticles were always found. The presence of a localized surface plasmon resonance in the nanoparticles was observed when SiO₂ and amorphous silicon were the host materials. Optical spectroscopy revealed that the localized surface plasmon resonance is at approximately 5.5 eV for tin nanoparticles in SiO₂, and at approximately 2.5 eV in amorphous silicon. The size of the tin nanoparticles in SiO₂ can be varied by changing the tin content of the films; this was used to tune the localized surface plasmon resonance.     

Thermal decomposition of the solid phase of nitromethane: ab initio molecular dynamics simulations

The Car-Parrinello molecular dynamics simulations were employed to investigate thermal decomposition of the solid nitromethane. It is found that it undergoes chemical decomposition at about 2200?K under ambient pressure. The initiation of reactions involves both proton transfer and commonly known C-N bond cleavage. About 75 species and 100 elementary reactions were observed with the final products being H2O, CO2, N2, and CNCNC. It represents the first complete simulation of solid-phase explosive reactions reported to date, which is of far-reaching implication for design and development of new energetic materials.     

Simulation of α-Zr structural stability under pressure using the molecular dynamics method

The structural stability of α-Zr was studied using the molecular dynamics method in wide temperature and pressure ranges. The interatomic interaction was described by a pair potential calculated within the Animalu pseudopotential model. The potential parameters were selected using α-Zr phonon spectra. The features in the dynamics of the α-β and α-ω phase transitions at various temperatures and pressures were considered. The calculated hysteresis of forward and backward phase transitions and its pressure and temperature dependences are discussed. The data obtained were used to plot phase equilibrium lines in the P-T phase diagram.     

Sensitivity in the trajectory of long-range α-particle

The factors influencing the trajectory of long-range ??-particle in the cold ternary fission of ²⁵²Cf are discussed. The trajectory of the ??-particle is studied by considering the influence of the force on the ??-particle due to Coulomb and proximity potentials and is found to have sensitive dependence on the initial position and initial energy of the ??-particle. The sensitivity to initial conditions signifies the presence of deterministic chaos which is characterized by Lyapunov exponent (LE). The LE is calculated using Wolf??s algorithm and found positive which implies that the objectives of trajectory calculations are restricted.     

Dynamic-mechanical study of molecular motions in solid polyoxymethylene copolymers from 4 to 315°K

Variations in four mechanical relaxations in polyoxymethylene copolymers in the temperature range from 4 to 315°K are described as a function of comer size and amount. The 6 relaxation at 50°K is interpreted as being due to limited motions in defect crystals; the γ₂ relaxation, at ca. 175°K, is also associated with defect motion in the crystal; the γ₁ relaxation, at ca. 205°K, is suggested to involve motion of short segments in disordered regions; aad the β relaxation, at ca. 270°K, involving motion of long segments, can be considered to be the glass transition.     

Electronic effects on radiation damage in α-iron:A molecular dynamics study

Iron(Fe)-based alloys, which have been widely used as structural materials in nuclear reactors, can significantly change their microstructure properties and macroscopic properties under high flux neutron irradiation during operation,thus, the problems associated with the safe operation of nuclear reactors have been put forward naturally. In this work, a molecular dynamics simulation approach combined with electronic effects is developed for investigating the primary radiation damage process in α...     

The investigation of solid–solid phase transformation at CuAlNi alloy using molecular dynamics simulation

In this study the thermodynamic and structural properties of a CuAlNi model alloy (3A) system were investigated using a molecular dynamics (MD) simulation method. The interactions between atoms were modelled by the Sutton-Chen embedded atom method (SCEAM) based on many-body interactions. It was observed that at the end of thermal process the thermo-elastic phase transformation occurred in the model alloy system. In order to analyse the structures obtained from MD simulation, techniques such as thermodynamic parameters and radial distribution function (RDF) were used. The local atomic order in the model alloy was analysed using Honeycutt–Andersen (HA) method.     

The origin of the pseudogap in α-Ga

Density functional theory, the free-electron empty lattice approximation and the nearly free-electron approximation are employed to investigate the electronic properties of partially covalent α-Ga. Whereas free-electron-like properties are revealed over a large energy range, a deep pseudogap at the Fermi level is characteristic of α-Ga. We explain the origin of the pseudogap in terms of a delicate interplay between the electronic states and the specific Brillouin zone geometry.     

Wavelet Correlation in the One-Dimensional Projection α-Model

One-dimensional projection of two-dimensional self-affine phase space for two typical self-affine fractals is studied,and one-dimensional projection α model is obtained.About this model,starting from characterstic function,we study its correlation densities and the wavelet correption moment.The wavelet basis functions of split number Λ=2,3,4 are found out.It turns out that the various wavelet-coefficents decouple when the second order wavelet correlation moments are considered.This is a general conclusion and model independent.