Direct and inverse computation of Jacobi matrices of infinite iterated function systems

We introduce a new set of algorithms to compute the Jacobi matrices associated with invariant measures of infinite iterated function systems, composed of one–dimensional, homogeneous affine maps. We demonstrate their utility in the study of theoretical problems, like the conjectured almost periodicity of such Jacobi matrices, the singularity of the measures, and the logarithmic capacity of their support. Since our technique is based on a reversible transformation between pairs of Jacobi matrices, it can also be applied to solve an inverse/approximation problem. The proposed algorithms are tested in significant, highly sensitive cases: they perform in a stable fashion, and can reliably compute Jacobi matrices of large order.     

Damping of the surface plasmon in clean and K-modified Ag thin films

The damping processes of electronic collective excitations of Ag/Ni(1 1 1) were studied by high-resolution electron energy spectroscopy. The FMHM of the Ag surface plasmon was reported as a function of Ag thickness, primary electron beam energy, Ag surface plasmon energy, and parallel momentum transfer. The broadening of the Ag surface plasmon was found to be related to 5sp–5sp transitions, for which a critical wave vector of 0.2 Å⁻¹ exists. Moreover, we provide a direct evidence of the occurrence of chemical interface damping in thin films, upon doping the Ag/Ni(1 1 1) system with K adatoms. The enhanced plasmon broadening in K/Ag/Ni(1 1 1) was ascribed to the existence of additional electron–hole decay channels at the K/Ag interface.     

Coarse-graining stiff bonds

The method of constraints in molecular dynamics is useful because it avoids the resolution of high frequency motions with very small time steps. However, the price to pay is that both the dynamics and the statistics of a constrained system differ from those of the unconstrained one. Instead of using constraints, we propose to dispose of high frequency motions by a coarse-graining procedure in which fast variables are eliminated. These fast variables are thus modeled as friction and thermal fluctuations. We illustrate the methodology with a simple model case, a diatomic molecule in a monoatomic solvent, in which the bond between the atoms of a diatomic molecule is stiff. Although the example is very simple and does not display the interesting effects of “wrong” statistics of the constrained system (i.e. the well-known issue connected to the Fixman potential), it is well suited to give the proof of concept of the whole procedure.     

Parity of the weak Fréedericksz transition

The European Physical Journal E - Motivated by the recent experimental findings by Kumar et al. (Phys. Rev. E., 82, 011701 (2010)) in which the inverse Fréedericksz transition is observed, we...     

Pressure effects on icosahedral short range order in undercooled copper

There is not a wide consensus on the role played by the icosahedral short range order on the stability of undercooled simple metals. The scenario is even less clear for undercooled metals under external pressure. Classical molecular dynamics simulations are performed to explain experimental results recently obtained on liquid and undercooled liquid copper under pressure. The atomic configurations are characterized by a common neighbor analysis to reveal the icosahedral short range order and its relation with external pressure. External pressure increases the probability to find atomic bonds with icosahedral symmetry both in the liquid and in the undercooled copper.     

Nucleation and growth mechanisms of Fe on Au(111) in the sub-monolayer regime

The growth of Fe on Au(111) at 300 K in the sub-monolayer regime has been investigated using scanning tunneling microscopy, focusing on the mechanisms of nucleation, coalescence and interlayer diffusion. Below a coverage of 0.1 ML, Fe growth proceeds in a well-ordered fashion producing regular arrays of islands, while approaching the island coalescence threshold (above 0.35–0.4 ML), we observed a consistent increasing of random island nucleation. These observations have been interpreted through rate equation models for the island densities in the presence of preferred nucleation sites. The evolution of the second layer fraction has also been interpreted in a rate equation scheme. Our results show that the ordered to random growth transition can be explained by including in the model bond breaking mechanisms due to finite Fe–Fe bond energy. A moderate interlayer diffusion has been inferred from data analysis between the second and the first layer, which has been used to estimate the energy barrier of the adatoms descending process.     

The Three-Wave Resonant Interaction Equations: Spectral and Numerical Methods

The spectral theory of the integrable partial differential equations which model the resonant interaction of three waves is considered with the purpose of numerically solving the direct spectral problem for both vanishing and non vanishing boundary values. Methods of computing both the continuum spectrum data and the discrete spectrum eigenvalues are given together with examples of such computations. The explicit spectral representation of the Manley-Rowe invariants is also displayed.     

Application of robust color composite fringe in flip-chip solder bump 3-D measurement

This study developed a 3-D measurement system based on flip-chip solder bump, used fringes with different modulation intensities in color channels, in order to produce color composite fringe with robustness, and proposed a multi-channel composite phase unwrapping algorithm, which uses fringe modulation weights of different channels to recombine the phase information for better measurement accuracy and stability. The experimental results showed that the average measurement accuracy is 0.43μm and the standard deviation is 1.38 µm. The results thus proved that the proposed 3-D measurement system is effective in measuring a plane with a height of 50 μm. In the flip-chip solder bump measuring experiment, different fringe modulation configurations were tested to overcome the problem of reflective coefficient between the flip-chip base board and the solder bump. The proposed system has a good measurement results and robust stability in the solder bump measurement, and can be used for the measurement of 3-D information for micron flip-chip solder bump application.     

Electronic properties of (3/2 × 3/2)-Na/Cu(1 1 1)

High-resolution electron energy loss spectroscopy was used to study the electronic properties of (3/2 × 3/2)-Na/Cu(1 1 1) at room temperature. Loss spectra showed two-well distinct losses at 114 and 180 meV assigned to not dispersive charge density waves. Mechanisms to explain their existence are proposed. Moreover, the expected 2D plasmon of the Na quantum well state was not observed. The strong influence of the underlying Cu substrate may be responsible for the absence of such mode.     

Taxonomy of correlations of wind velocity — an application to the Sicilian area

We present an algorithm that allows us to analyze the cross-correlation of wind velocity measured in different locations; this algorithm is applied to 29 recording stations in Sicily. The results show that such correlations present a significant and persistent ultrametric structure that is influenced by the geographical neighborhood as well as by the presence of mountain and the sea. The algorithm presented, that is also able to reveal weak correlations, can be used as a starting point for the development of multivariate models of wind.