Green's functions on finite lattices and their connection to the infinite lattice limit

It is shown that the Green's function on a finite lattice in arbitrary space dimension can be obtained from that of an infinite lattice by means of translation operator. Explicit examples are given for one- and two-dimensional lattices

Phase locked harmonic generation in the opaque region of GaAs

We demonstrate second and third harmonic generation from a GaAs substrate, well-below the absorption edge, in both transmission and reflection geometries. The pump is tuned at 1064 nm, in the transparency range, while the SH and the TH signals are tuned in the opaque spectral range of GaAs, at 532 nm and 355 nm, respectively. As expected, we find that the polarization of the generated signals is sensitive to the polarization of the pump. In our experiment, we work far from the phase matching condition and we account for both surface and bulk contributions, and show that the surface-generated SH components can be more intense than bulk-generated SH signals. The experimental results are contrasted with numerical simulations that include these two factors, using a hydrodynamic model that accounts for all salient aspects of the dynamics, including surface and bulk generated harmonic components.Peer ReviewedPostprint (published version

On the Effective Elastic Properties of Macroscopically Isotropic Media Containing Randomly Dispersed Spherical Particles

computational scheme for estimating the effective elastic properties of a particle reinforced matrix is investigated. The randomly distributed same-sized spherical particles are assumed to result in a composite material that is macroscopically isotropic. The scheme results in a computational efficient method to establish the correct bulk and shear moduli by representing the three-dimensional (3D) structure in a two-dimensional configuration. To this end, the statistically equivalent area fraction is defined in this work, which depends on two parameters: the particle volume fraction and the number of particles in the 3D volume element. We suggest that using the statistically equivalent area fraction,introduced and defined in this work, is an efficient way to obtain the effective elastic properties of an isotropic media containing randomly dispersed same-size spherical particles

Assessing Plastically Dissipated Energy as a Condition for Fatigue Crack Growth

The suitability of using a proposed condition for simulating cyclic crack propagation in a numerical scheme is qualitatively investigated, employing the finite element method. The propagation criterion is based on a condition that relates the plastically dissipated energy to a critical value. In the finite element simulation scheme, the crack is allowed to propagate when the criterion is satisfied, and the crack propagates until the condition is no longer fulfilled. Experimentally, it is well established that a negative load ratio increases the crack propagation rate, whereas a tensile overload tends to decrease the crack propagation rate. By simulating these load conditions, we show that the proposed propagation criterion closely captures these rate changes

A Simple Numerical Method of Cycle Jumps for Cyclically Loaded Structures

A method for accelerated numerical simulations of structures subjected to cyclic loading is investigated. Of particular interest is a class of structures where the structural properties evolve with time. The proposed method is based on conducting detailed finite element analysis for a set of cycles to establish a trend line, extrapolating the trend line spanning many cycles, and use the extrapolated state as initial state for additional FEA simulations. This includes a control function that automatically monitors the length of the cycle jump to ensure a realistic solution. We compare the proposed method to a reference calculation, where all incremental cycles are conducted, and find that the cycle jump solution replicates the true solution

Study on the Relationship between the Efficiency of the Actions in the Game and the Result of the Match

The paper wants to highlight the connection between the efficiency of the game actions, i.e. the level of the players' technique, and the final result of the game. The main purpose of this research was to emphasize and present the importance of efficient in-game actions, which have the role of determining the outcome of the match. The study was conducted on all participants in the National Volleyball Championship of Romania, male 2021/2022. Analysis of the game variables (serve, serve reception, set, and spike and attack reception) and game outcome were performed through the 1992 FIVB recording system, which confirmed the study's hypothesis that increased player efficiency leads to winning games

An Object-Oriented Approach for Modeling and Simulation of Crack Growth in Cyclically Loaded Structures

We present an object-oriented modeling frame for simulating crack propagation due to cyclic loadings. Central to the approach is that the crack propagates when a user-defined propagation criterion is fulfilled, i.e., the crack propagation rate is not prescribed but predicted. The approach utilizes the commercial finite element software package ABAQUS and its associated Python based scripting interface. The crack propagation is simulated by a generalized node release technique. If the propagation criteria are satisfied in the end of a cycle, the crack is allowed to propagate. The incremental crack growth is inferred from an iterative investigation of the propagation criteria. The propagation criteria are user-defined, and can be based on any parameter or parameter set that can be obtained from the simulations. We illustrate the developed modeling frame by two benchmark problems, where the propagation criterion is based on the dissipated energy in the vicinity of the crack tip

Anomalous bond stretching phonons as a probe of charge fluctuations in perovskites

Important information on momentum resolved low energy charge response can be extracted from anomalous properties of bond stretching in plane phonons observed in inelastic neutron and X-ray scattering in cuprates and some other perovskites. We discuss a semiphenomenological model based on coupling of phonons to a single charge mode. The phonon dispersion and linewidth allow to locate the energy of the charge excitation in the mid infrared part of the spectrum and to determine some of its characteristics. New experiments on oxygen isotope substitution could allow to achieve a more detailed description. Corresponding relations following from the model can be used for the interpretation of experiments and as test of the model.Comment: presented at the M2S-HTSC-VIII conference in Dresde

Resonant, broadband and highly efficient optical frequency conversion in semiconductor nanowire gratings at visible and UV wavelengths

Using a hydrodynamic approach we examine bulk- and surface-induced second and third harmonic generation from semiconductor nanowire gratings having a resonant nonlinearity in the absorption region. We demonstrate resonant, broadband and highly efficient optical frequency conversion: contrary to conventional wisdom, we show that harmonic generation can take full advantage of resonant nonlinearities in a spectral range where nonlinear optical coefficients are boosted well beyond what is achievable in the transparent, long-wavelength, non-resonant regime. Using femtosecond pulses with approximately 500 MW/cm2 peak power density, we predict third harmonic conversion efficiencies of approximately 1% in a silicon nanowire array, at nearly any desired UV or visible wavelength, including the range of negative dielectric constant. We also predict surface second harmonic conversion efficiencies of order 0.01%, depending on the electronic effective mass, bistable behavior of the signals as a result of a reshaped resonance, and the onset fifth order nonlinear effects. These remarkable findings, arising from the combined effects of nonlinear resonance dispersion, field localization, and phase-locking, could significantly extend the operational spectral bandwidth of silicon photonics, and strongly suggest that neither linear absorption nor skin depth should be motivating factors to exclude either semiconductors or metals from the list of useful or practical nonlinear materials in any spectral range.Comment: 12 pages, 4 figure