Diamond-graphite phase transition in ultradisperse-diamond clusters

A systematic study of the diamond-graphite structural phase transition in ultradisperse-diamond clusters obtained by the detonation technique is reported. Samples of two types, differing in the kinetics of detonation-product cooling, were investigated. The phase transition was achieved under heating in an inert atmosphere in the temperature range 720–1400 K. The transition was identified by Raman scattering and x-ray diffraction data. Raman and x-ray characterization showed the ultradisperse diamond, irrespective of the cooling rate used, to be cluster material possessing diamond structure with a characteristic nanocrystal size of 43 Å. The diamond-graphite phase transition in ultradisperse diamond is shown to start from the cluster surface inwards at T _pt≈1200 K, i.e. at substantially lower temperatures than is the case with bulk diamond single crystals.     

Fractal structure of gold clusters formed under vacuum deposition on dielectric substrates

The growth of gold island films under vacuum deposition on the surface of dielectric substrates are investigated. Fractal dimensions of the clusters formed under film deposition at different substrate temperatures and evaporation rates are estimated. The correlation between surface morphology and optical properties of the films deposited are discussed.     

Fractal geometry of critical Potts clusters

Numerical simulations on the total mass, the numbers of bonds on the hull, external perimeter, singly connected bonds and gates into large fjords of the Fortuin-Kasteleyn clusters for two-dimensional q-state Potts models at criticality are presented. The data are found consistent with the recently derived corrections-to-scaling theory. A new method for thermalization of spin systems is presented. The method allows a speed up of an order of magnetization for large lattices. We also show snapshots of the Potts clusters for different values of q, which clearly illustrate the fact that the clusters become more compact as q increases, and that this affects the fractal dimensions in a monotonic way. However, the approach to the asymptotic region is slow, and the present range of the data does not allow a unique identification of the exact correction exponents.Received: 2 June 2003, Published online: 9 September 2003PACS: 05.50.+q Lattice theory and statistics (Ising, Potts, etc.) - 05.45.Df Fractals - 75.10.-b General theory and models of magnetic ordering - 75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)     

Fractal structure of fullerite

We have obtained macroscopic fractal aggregates of fullerite ranging in size from 100 to 400 μm. The fractal structure of fullerite is formed by microscopic (30–100 nm) fullerite crystals in the presence of a temperature gradient under conditions of diffusion-limited aggregation. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 684–685 (10 May 1998)     

The structure of para-hydrogen clusters

The path integral Monte Carlo calculated radial distributions of para-hydrogen clusters $({\rm p}\text{-}{\rm H}_2)_N$ consisting of N = 4-40 molecules interacting via a Lennard-Jones potential at $T=1.5~{\rm K}$ show evidence for additional peaks compared to radial distributions calculated by diffusion Monte Carlo ( $T=0~{\rm K}$ ) and path integral Monte Carlo at $T \leq 0.5~{\rm K}$ . The difference in structures is attributed to quantum delocalization at the lowest temperature. The new structures at finite temperatures appear to be consistent with classical structures calculated for an effective Morse potential, which in order to account for the large zero point energy, is substantially softer than the Lennard-Jones potential.     

Electronic structure of BiSeI clusters

The valence band (VB) energy levels of BiSeI crystals have been calculated and compared to the X-ray photoelectron spectra of SbSI crystals. A molecular cluster consisting of 20 molecules of BiSeI has been used to calculate the total VB density of states by the density functional theory (DFT) method. The spectrum of total VB density of states of the (BiSeI)₂₀ cluster weighted by atomic photoemission cross-sections has been compared with the experimental X-ray photoelectron VB spectrum of SbSI type crystals. The cluster model calculation has showed that the core level energy splitting depends on the difference of ionic charges of the same atoms at the edges of the (BiSeI)₂₀ cluster.     

Fractal structure of marine measuring networks

Summary This paper deals with the fractal character of several distribution points measuring the Earth's total magnetic field (ETMF) during some marine surveys that we carried out in the Gulf of Pozzuoli and around the island of Ischia (Naples, Italy). Previous studies evaluated the fractal dimension of networks constituted by fixed measuring stations. The examined distributions display a ?fractal scaling? regime on 3–4 decades of distances with fractal dimensions of 1.80 and 1.54. These values characterize the whole investigated area covered by the distribution of experimental data. Linked to fractal dimension is the possibility of reconstructing the field and the capacity to reveal sparse and intense phenomena (e.g. magnetic anomalies) with a low fractal dimension. In distributions with large areas without measuring points, Shannon's theorem is no longer applicable in 2D. The fractal evaluation enables a spatial limit to record the phenomena to be defined and therefore establishes the minimum wavelength recordable of the magnetic field.     

Fractal structure of artificial ionospheric turbulence

We show the results of the first experimental studies of the multifractal structure of the developed artificial ionospheric turbulence. As a result of the special multifractal analysis of the recorded amplitudes of signals from the orbital satellites, which were obtained during the experiments on radio tomography of the irregularities excited in the ionosphere by the powerful mid-latitude heating facility “Sura,” it is found that the characteristic multifractal structure of these records is caused by the nonuniform spatial distribution of the small-scale fluctuations of the electron number density in the artificial irregularities of the ionospheric plasma. Comparative analysis is performed for the multifractal spectra of fluctuations of both the amplitudes and energies of signals received from the orbital satellites upon radio transmission probing of the region of artificial ionospheric turbulence by these signals at three observation points located near the “Sura” heating facility and spaced apart to a distance of about 100–150 km. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 11, pp. 970–976, November 2008.     

Fractal structure of eigenmodes of unstable-cavity lasers

We show that the eigenmodes of unstable-cavity lasers have fractal structure, in contrast with the well-known stable-cavity eigenmodes. As with all fractals, the dynamic range over which self-similarity holds is limited; in this case the range is set by diffraction, i.e., by the Fresnel number of the resonator. We determine the fractal dimension of the mode profiles and show that it is related to the aperture shape.     

Electronic structure of hexagonal quantum—disc clusters

Within the effective-mass approximation,we investigate the electronic structure of hexagonal quantum-disc clusters using the finite element method.With an increasing amount of quantum dots in the cluster,the electronic energy levels quickly expand into mini-bands.each consisting of discrete,unevenly distributed energy levels,The corresponding electronic eigenfunctions are linear combinations of the electron orbits in each quantum dot.The spatial symmetry of the combination is the same as the electronic eigenfunctioin of a single quantum dot.     

The structure of mixed nitrogen-argon clusters

Using realistic pair potentials, we investigate the structures of mixed clusters of argon and nitrogen in order to interpret the experimental electron diffraction patterns reported by the Torchet group. Simulations of small clusters indicate that argon tends to segregate at the center of the clusters. For larger clusters, in the range of 50 to 200 molecules, MC methods have been used to simulate structures that are likely to be generated in the molecular beam. By comparing predicted electron diffraction patterns with those recorded in the experiments, our models allow us to estimate the average size and composition of the mixed clusters for a given set of experimental conditions (nozzle stagnation pressure and Ar partial pressure).     

Fractal structure of hyperbolic Lipschitzian dynamical systems

In the paper, dynamical systems admitting no smooth structure are studied. A theorem on the semiconjugacy of a Lipschitzian dynamical system to the corresponding topological Markov chain is proved. A new approach to evaluating bounds for the Hausdorff and the Kolmogorov dimensions of the set of nonwandering points from a Markov partition is suggested.     

Fractal structure of zeros in hierarchical models

We consider an Ising and aq-state Potts model on a diamond hierarchical lattice. We give pictures of the distribution of zeros of the partition function in the complex plane of temperatures for several choices ofq. These zeros are just the Julia set corresponding to the renormalization group transformation.     

Fractal clusters and self-propagating high-temperature synthesis in thin Al/Ge films

Fractal clusters in amorphous thin films are examples of growth models. The main models are the Witten-Sander model and its modifications. It is believed that fractal patterns are formed in the course of the crystallization of an amorphous phase. It is shown that self-propagating high-temperature synthesis can be initiated in an Al/Ge film system and fractal patterns are formed in the reaction products. It is conjectured that the transition of an amorphous phase to a crystalline phase does not play a substantial role in the appearance of such patterns, while the formation of fractal clusters is determined by self-propagating high-temperature synthesis. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 5, 317–321 (10 March 1998)