Quasi-lattice model for the thermodynamic properties and microscopic structure of molten Fe-Si alloy

The quasi-lattice model has been used to study the concentration dependant thermodynamic properties and microscopic structure of Fe-Si alloys in molten state. We have determined the free energy of mixing, excess entropy of mixing, the concentration-concentration structure factor in long wavelength limit [S_CC(0)] and the Warren-Cowley short range order parameter (α₁) of Fe-Si liquid alloy at 1873 K. The observed asymmetry in the properties of mixing of Fe-Si alloy in molten state is successfully explained on the basis of the quasi-lattice model. The analysis suggests that the Fe₂Si complexes are most likely to exist in the liquid state and are strongly interacting in nature. The theoretical analysis suggests that the pairwise interaction energies between the species depend considerably on temperature and the alloy is more ordered towards Fe rich region.     

Evolution of the structure and thermodynamic stability of the BaTiO3(001) surface

We report a series of new surface reconstructions on BaTiO3(001) as a function of environmental conditions, determined via scanning tunneling microscopy and low energy electron diffraction. Using density functional theory calculations and thermodynamic modeling, we construct a surface phase diagram and determine the atomic structures of the thermodynamically stable phases. Excellent agreement is found between the predicted phase diagram and experiment. The results enable prediction of surface structures and properties under the entire range of accessible environmental conditions.     

The representation of thermodynamic properties at high pressures

It is sometimes advantageous to have an expression for the Gibbs energy, G_m(T,P), from which one can analytically derive an expression for the Heimholtz energy, F_m(T, V_m). Such an expression is suggested for solid substances and it is shown how expressions for other physical properties can be derived from it.     

Evolution of III-V nitride alloy electronic structure: the localized to delocalized transition

Addition of nitrogen to III-V semiconductor alloys radically changes their electronic properties. We report large-scale electronic structure calculations of GaAsN and GaPN using an approach that allows arbitrary states to emerge, couple, and evolve with composition. We find a novel mechanism of alloy formation where localized cluster states within the gap are gradually overtaken by a downwards moving conduction band edge, composed of both localized and delocalized states. This localized to delocalized transition explains many of the hitherto puzzling experimentally observed anomalies in III-V nitride alloys.     

Spin structure of the pion in a light-cone representation

The spin structure of the pion is discussed by transforming the wave function for the pion in the naive quark model into a light-cone representation. It is shown that there are higher helicity (λ ₁+λ ₂=±1) states in the full light-cone wave function for the pion besides the ordinary helicity (λ ₁+λ ₂=0) component wave functions as a consequence from the Melosh rotation relating spin states in light-front dynamics and those in instantform dynamics. Some low energy properties of the pion, such as the electromagnetic form factor, the charged mean square radius, and the weak decay constant, could be interrelated in this representation with reasonable parameters.     

Pb-Sn合金及Pb的热力学性质的第一性原理计算

本文基于第一性原理的密度泛函理论(DFT)和密度泛函微扰理论(DFPT)方法,利用虚晶近似的计算方法研究了Pb-Sn合金的晶格结构、电子能带、声子能带及热力学性质,并用晶格能量差可与达到熔化温度时的振动能量相当的固-液相变机理研究了熔化温度,同时与所计算Pb的所有结果进行了对比.     

Magnetic structure and thermodynamic properties of TmPtIn

Physical properties of TmPtIn have been investigated by means of magnetic, electrical transport, calorimetric as well as neutron diffraction measurements. The compound crystallizes in the hexagonal ZrNiAl-type crystal structure. It orders antiferromagnetically below T_N = 3.5 K with the Tm magnetic moments confined to the basal hexagonal plane. They form a non-collinear “triangular” magnetic structure that may be described by the propagation vector . At 1.6 K, the Tm magnetic moment is equal to 5.59(9)μ_B. The antiferromagnetic character of the electronic ground state is reflected in the low temperature behaviors of the magnetic susceptibility and the specific heat, which may be described by spin-wave theory of antiferromagnetic magnons with linear dispersion relation. The compound exhibits metallic character of electrical conduction.     

Specific features of the hydrogen-induced discrete (jumplike) structural evolution in Pd-Ta-H and Pd-Mo-H alloys

The nonmonotonic structural evolution observed in Pd-Ta-H and Pd-Mo-H hydrogenated alloys is shown to be discrete (jumplike) in character, which is due to the thermodynamic potential having a multivalley fractal structure in reciprocal space. This structure arises in the initial state and is fairly stable. Transformations occur as a result of hopping of the system between the long-lived states corresponding to local minima of the thermodynamic potential at both stages of rapid degassing and of stochastic oscillations of the centroids of diffraction maxima. The jumps are associated with the migration of hydrogen atoms and vacancies between the matrix and defect complexes and are accompanied by an increase or a decrease in the diffraction angles.     

Evolution of the dislocation structure and the stage of work-hardening of Ni3Fe alloy with [001] orientation

Using transmission diffraction electron microscopy, the dislocation structure of work-hardened iron nickel alloy with the compression axis in [001] orientation is studied over a wide interval of gradual strain. A connection is established between the change of the flow curve and the type of substructure formed. The quantitative characteristics of the observed structural types are determined and their behavior at different stages of the strain curve is traced.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 18–24, February, 1988.     

Possible thermodynamic structure underlying the laws of Zipf and Benford

We show that the laws of Zipf and Benford, obeyed by scores of numerical data generated by many and diverse kinds of natural phenomena and human activity are related to the focal expression of a generalized thermodynamic structure. This structure is obtained from a deformed type of statistical mechanics that arises when configurational phase space is incompletely visited in a strict way. Specifically, the restriction is that the accessible fraction of this space has fractal properties. The focal expression is an (incomplete) Legendre transform between two entropy (or Massieu) potentials that when particularized to first digits leads to a previously existing generalization of Benford’s law. The inverse functional of this expression leads to Zipf’s law; but it naturally includes the bends or tails observed in real data for small and large rank. Remarkably, we find that the entire problem is analogous to the transition to chaos via intermittency exhibited by low-dimensional nonlinear maps. Our results also explain the generic form of the degree distribution of scale-free networks.     

Calculation of the vortex structure in a superconducting alloy

We calculate properties of an isolated vortex in a dirty BCS superconductor at zero temperature by numerical integration of a diffusion equation. This is supplemented by a self-consistency equation for the order parameter, and we show that a simple trial form gives quite a good solution of it. The electronic density of states and low temperature specific heat are also calculated for extreme type II material. The difference between the density of states at frequencies ω and 0 is proportional to ω² for small ω, and the specific heat is similar to that predicted by previous approximate theory.     

Evolution of the nucleon structure in the lightest nuclei

We show that the pattern of the oscillation of the structure functions ratio r^A(x)=F₂^A/F₂^N(D) varies with A by changing the position of the cross-over point x₃ in which r^A(x)=1, unlike the pattern for nuclei with masses A>4, where only the amplitude of the oscillation changes. In particular we find that the pattern of F₂(x) modifications is controlled with the values (1−x₃)=0.32 (D/N), 0.16 (³He/D) and 0.08 (⁴He/D). The obtained results follow from the relativistic approach and allow one to define the class of modifications of the bound nucleon structure.     

Evolution of structure in exotic nuclei

Nuclear structure in exotic nuclei is likely to be quite different than in the nuclei we have been able to access near the valley of stability. With the development of advanced radioactive-beam facilities, we will, for the first time, have access to long isotopic chains of nuclei. A key facet of exotic nuclei therefore will be the study of the evolution of structure with N, Z, and A to an extent never before imagined. Yet, the beam intensities will be very low (relative to stable beams); hence, we will need to extract more physics from less data. We will discuss several aspects of structural evolution and its elucidation in exotic nuclei.     

Domain structure of Fe-N alloy

Observations of domain structures in single crystal and polycrystalline samples of Fe-N alloy were made. It was found that the magnetization direction is perpendicular to the surface of Fe₁₆N₂ nitrides. The domain structure is not subject to essential changes during ageing.     

Inhomogeneity in structure of MgPb liquid alloy

The concentration dependent asymmetry in mixing properties of MgPb liquid alloys at 973 K has been investigated on the basis of regular associated solution model. The analysis suggests that heterocoordination leading to the formation of chemical complex Mg₂Pb is likely to exist in the melt.     

Evolution of local atomic structure in a melt-spun Ni25Ti50Cu25 shape memory alloy during crystallization

The local atomic environment of a melt-spun Ni₂₅Ti₅₀Cu₂₅ amorphous alloy and bond evolution during crystallization were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and differential scanning calorimetry. In the amorphous alloy, the interatomic distances of Ni–Ti and Cu–Ti are distinct from Ti–Ti and can be indicative of the formation of two types of dominant polyhedra or distorted polyhedral clusters centered with Ni and Cu, with the majority of shell atoms being Ti. The overall increase in the coordination numbers of Ni, Ti, and Cu by crystallization and evidence for structural relaxation suggest that the melt-spun ribbon contains a combination of ordered structures and free volume prior to the heat treatment. Copper and nickel are co-located as their absorption spectra are similar. Although crystallization occurs rapidly (within 4?min at 500 °C), the local atomic environment change persists at longer annealing durations (up to 10?min). An increase in the Ti–Ti and Cu–Cu homo-bond fractions at short and intermediate annealing times suggests that these species segregate between Cu-rich and Cu-poor phases. Crystallization continues through a short-range Ti and Cu diffusion-dominated process, as the near-neighbor structures of Ti and Cu change considerably more than for Ni during annealing. This homogenizes the microstructure followed by possible precipitation of a TiCu compound.     

Evolution of community structure in the world trade web

In this note we study the bilateral merchandise trade flows between 186 countries over the 1948–2005 period using data from the International Monetary Fund. We use the network visualization package Pajek to identify network structure and behavior across thresholds and over time. In particular, we focus on the evolution of trade “islands” in a world trade network in which countries are linked with directed edges weighted according to the fraction of total dollars sent from one country to another. We find mixed evidence for globalization.     

Discrete representation of perceptual structure underlying consonant confusions

The perceptual representation of speech is generally assumed to be discrete rather than continuous, pointing to the need for general discrete analytic models to represent observed perceptual similarities among speech sounds. The INDCLUS (INdividual Differences CLUStering) model and algorithm [J.D. Carroll and P. Arabie, Psychometrika 48, 157-169 (1983)] can provide this generality, representing symmetric three-way similarity data (stimuli X stimuli X conditions) as an additive combination of overlapping, and generally not hierarchial, clusters whose weights (which are numerical values gauging the importance of the clusters) vary both as a function of the cluster and condition being considered. INDCLUS was used to obtain a discrete representation of underlying perceptual structure in the Miller and Nicely consonant confusion data [G.A. Miller and P.E. Nicely, J. Acoust. Soc. Am. 27, 338-352 (1955)]. A 14-cluster solution accounted for 82.9% of total variance across the 17 listening conditions. The cluster composition and the variations in cluster weights as a function of stimulus degradation were interpreted in terms of the common and unique perceptual attributes of the consonants within each cluster. Low-pass filtering and noise masking selectively degraded unique attributes, especially the cues for place of articulation, while high-pass filtering degraded both unique and common attributes. The clustering results revealed that perceptual similarities among consonants are accurately modeled by additive combinations of their specific and discrete acoustic attributes whose weights are determined by the nature of the stimulus degradation.