A model for vibrational properties of the atomic interface in A/B fcc metals

The motivation of this theoretical work is to introduce a model calculation for the elastic waves scattering and coherent phonon transport at an atomic nanojunction between face-centered cubic (fcc) leads. The model system A/B consists of two perfect semi-infinite fcc leads A and B, oriented in the same direction and joined by an atomic interface. It is applied to the system Cu/Ni and its inverse Ni/Cu. A theoretical approach based on the matching method is used to study the dynamics of the system A/B.     

Nucleation of kink pairs on partial dislocations: A new model for solution hardening and softening

Nucleation and motion of kink pairs on partial dislocations are examined by elasticity theory for materials with a high Peierls stress. Two approaches are used: one considers the change in average stacking-fault energy (SFE) due to alloying elements and the other considers the change in local SFE due to a nearby solute atom. Both approaches highlight the role of SFE on kink nucleation, propagation and annihilation and both furnish strain rate as a function of stress, temperature and SFE. Model predictions are compared with yield stress data for two systems: firstly, an intermetallic, MoSi₂, which softens for alloying elements (V, Nb, Cr and Al) that decrease the SFE and hardens for Re additions that increase the SFE; secondly, a ceramic oxide, MgO-Al₂O₃ spinel, which softens with increasing addition of excess alumina and at the same time exhibits a decrease in SFE. The average SFE approach agrees qualitatively with the data while quantitative agreement is obtained with the local SFE approach. The possibility is considered that the model applies to other materials, such as TiAl, HfV₂ and Fe₃Al, which show softening with certain alloying additions. One requirement is that the dislocations are dissociated more than a few atomic distances; otherwise kink nucleation occurs on the perfect dislocation (or simultaneously on both partials). Hence the model does not apply to materials such as bcc metals which only have a core dissociation. Normal hardening effects of solutes from size and modulus misfits are additive with any softening effects from a decrease in SFE and so may mask the latter, as occurs for W additions to MoSi₂.     

General regularities of interaction between halogens and surface of fcc metals

Main peculiarities of chemical interaction between halogens and fcc metals have been analyzed and results for chemical reaction on copper and silver surfaces as the most studied ones are discussed. General information about the structure of adsorbed layers on metal surfaces is presented. It has been shown that halogenation occurs in two stages. First, a monolayer of chemisorbed halogen atoms is formed, and then metal halide starts to grow, forming a continuous halide film on the surface. The chlorination of silver is indicated (on the basis of the spectroscopic data) as a unique case due to the possible chlorine dissolution into the substrate bulk. It has also been shown that the use of low-energy electron diffraction is usually ineffective for identification of incommensurate lattices at the stage of monolayer and halide film structure formation. To study incommensurate surface structures and halide nucleation processes on atomic scale, probe microscopy and methods for detecting local structure are necessary.     

New results on diffusion in fcc metals

The Kondo model for the diffusion of light particles in metals has provided a satisfactory explanation for the low temperature diffusion rates for muons in the fcc metals Cu and Al. Explicit experiments which show the strong dependence of muon behaviour on the presence of conduction electrons have now been performed belowT=1 K in Al. Challenging new diffusion studies on fcc metals such as Pt are also presented.     

The production of frenkel defects in fcc metals

Experimental results from polycrystalline and single crystalline samples of aluminum are analyzed in terms of how electron irradiation causes atomic displacements along 〈100〉 and 〈110〉 crystallographic directions. This interpretation is made for atoms that recoil with energies sliihtly greater than the threshold energy. It is noted that definite correlations exist between some of the substages of stage I and the natural required behavior of recoiling atoms. By applying this criterion to polycrystalline samples, one establishes a means for identifying other phenomena; e.g. multiple atomic displacements, spontaneous recombination, etc.     

Size effects in the hardness of fcc metals on micro- and nanoscales

The size effects in the hardness of three fcc metals, namely, Ni, Cu, and Al, are studied by micro- and nanoindentation, and the boundaries of regions with size effects of various types and the characters of these effects are determined.     

Two-dimensional numerical visualization on the interaction of blast waves with obstacles

In this study, the complex phenomena of propagation and interaction of the blast waves impacting on obstacles were visualized and investigated using a numerical method. Three different distances between an immovable wall and a bomb shelter with a square block inside were considered while a blast source is located in front of wall at the same distance from shelter. The transitional shock phenomena were simulated by means of a multi-block mesh system and a flux computational model. Spatial discretization was performed using the Roe’s upwind schemes; time integration was achieved via the second-order explicit Hancock method. Proof of the numerical results indicated that those results were in close agreement with the experimental data obtained for the wedge flow. For the cases proved, the geometries of the reflected wave patterns followed by the incident blast waves crossing the immovable wall and impacting inside of bomb shelters were similar. However the height of wall has a dominating impact on the effect associated with different incident blast waves from the same blast source. Meanwhile, different reflected overpressure-time histories and streamlines were observed and analyzed for the results obtained.     

Calculation of the surface energy of fcc metals with modified embedded-atom method

The surface energies for 38 surfaces of fcc metals Cu, Ag, Au, Ni, Pd, Pt, A1, Pb, Rh and Ir have been calculated by using the modified embedded-atom method. The results show that, for Cu, Ag, Ni, A1, Pb and Ir, the average values of the surface energies are very close to the polycrystalline experimental data. For all fcc metals, as predicted, the close-packed (111) surface has the lowest surface energy. The surface energies for the other surfaces increase linearly with increasing angle between the surfaces (hkl) and (111). This can be used to estimate the relative values of the surface energy.     

Interatomic interaction in interstitial solutions with fcc and bcc lattices

The energy and deformation interaction in disordered interstitial solutions are determined by means of the pseudopotential method. Calculations are made for the systems Ti-C and Zr-C. Comparison of the deformation interaction energies and the Fourier transforms of the quasielastic forces has shown that in the system Ti-C the deformation interaction is greater than in Zr-C. Numerical calculations have established that filling of the z sublattice of octahedral interstices is energetically more advantageous in the bcc interstitial solution Zr-C.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 79–83, January, 1981.     

Peculiarities of anharmonic effects in the lattice thermodynamics of fcc metals

Explicit expressions for anharmonic contributions to the thermodynamic properties with allowance for higher-order phonon–phonon interactions for closed-packed crystals are given, and the calculations for some fcc metals near the melting (Ir, Rh) and martensite phase transition (Ca, Sr) points are carried out. A detailed comparison of anharmonic and electron contributions to the heat capacity of these metals is carried out. The computational results for high-temperature heat capacity agree well with the available experimental data.     

Equivalence of the angular forces in the lattice dynamics of fcc metals

The expressions for the Clark, Gazis and Wallis type of angular forces are rederived in the caseof fcc metals. These expressions are now foundtobe equivalent to the deLauney type of angular forces.     

A new local and lorentz-covariant solution of the schwinger model

We present a local, manifestly Lorentz-covariant operator solution of the Schwinger model for arbitrary gauge. The main features of our solution are: (i) there is a unique normalizable translation-invariant state, (ii) the electric and chiral charge are not spontaneously broken, i.e. they generate implementable symmetry transformations, (iii) on the physical subspace the vacuum is degenerate in energy with an infinite number of states of nonzero chirality, (iv) the electromagnetic tensor is simply proportional to a massive pseudo-scalar field.     

Characteristic features of anharmonic effects in the lattice dynamics of fcc metals

The dispersion in the entire Brillouin zone and the temperature dependence (right up to the melting temperature) of the anharmonic frequency shift and phonon damping in a number of fcc metals is investigated on the basis of microscopic calculations. It is found that the anharmonic effects depend sharply on the wave vector in the directions Г-X, X-W, and Г-L and, in contrast to bcc metals, the magnitude of the effects is not due to the softness of the initial phonon spectrum. It is shown that the relative frequency shifts and the phonon damping near melting do not exceed 10–20%. The relative role of various anharmonic processes is examined, and the relation between the results obtained and existing experimental data is discussed. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 9, 649–652 (10 May 1999)     

fcc金属层错能的EAM法计算

采用嵌入原子法(EAM)计算了Cu，Ag，Au，Ni，Al，Rh，Ir，Pd，Pt和Pb等10种面心立方(fcc)金属的层错能，除Rh和Ir两种金属外，其他金属的计算结果和实验结果基本一致. 关键词： 面心立方金属 层错能 EAM     

Equation of state and thermodynamics of fcc transition metals: A pseudopotential approach

A simple pseudopotential model is used for the calculation of the phonon spectra at the equilibrium volume and under pressure. The model is based on the secondorder perturbation theory with the local pseudopotential acting on thes electrons while thed electrons contribution is simulated by the repulsive Born-Mayer interatomic potential. Pressure influence on the lattice properties was studied for small compressions (mode Grüneisen parameters) as well as for ultrahigh pressure (equation of state up to 1 TPa). Results of the lattice dynamics calculations were used for determining temperature dependence of the lattice heat capacity and of the macroscopic Grüneisen parameter. The Kohn anomaly at the small wave vectors obtained previously in palladium, platinum and rhodium affects strongly the temperature dependence at low temperature.     

On the role of solute atom — dislocation elastic interaction in solid solution hardening of Cu single crystals

Elastic interaction of solute atoms with dislocations has been reconsidered in Labusch's theory of solid solution hardening. New interaction parametersε are suggested and tested on dΤ/dc ^2/3 dependence onε ^4/3 for Cu base solid solutions.     

A new endocytic model based on the co-rotational grid method

Endocytosis plays important roles in many cellular physiological processes, such as metabolism and immune. Many theoretical models have been proposed to study the endocytic process, but little has considered the tensile deformation of the membrane and the actin forces. In this paper, a new endocytic model is proposed based on the co-rotational grid method. Our model gives a direct estimation of the in-plane strain of the plasma membrane and provides a basis for the calculation of further scission process of the vesicle. The results fit well with experimental data in the literature. Moreover, it is suggested that the active forces of actin at the endocytic site is the main mechanism driving the invagination of the plasma membrane.     

Influence of surface stress in the missing row reconstruction of fcc transition metals

Surface stress relief is often invoked as the driving force for surface reconstruction. The present ab initio total energy calculations show that it is not the case, at least for the missing row reconstruction undergone by the (1 1 0) surface of the face centered cubic transition metals. Instead, they show that the tendency to reconstruct or not is closely related to the sign and magnitude of the strain derivative of surface energy. Finally, they unambiguously confirm that relativistic effects are at the origin of this reconstruction.     

The heat of solution and interaction effects for noble gas atoms in metals

A simple model is presented from which the enthalpy of solution of noble gases in arbitrary metals can be estimated quantitatively.The heat of solution is derived as the interfacial energy at the contact interface between the metal and a noble gas atomic cell in solution.The model picture offers an explanation for the strong attraction between noble gas atoms, in particular helium, and vacancies, other noble gas atoms or metallic impurities with a low surface energy.