The LiNbO(3) congruent crystals doped with small Nd concentrations, <1 mol% Nd, and co-doped with Mg ions, 0-9 mol% Mg, were systematically investigated by means of micro-Raman spectroscopy in the Y and Z crystal directions. Results obtained from an undoped congruent crystal, an Nd-doped crystal, a Mg-doped crystal and Nd, Mg-co-doped crystals are compared. From the analyses of the results obtained in the Y direction, the Nd and Mg content dependence of the two lowest-Raman A(1)(TO(1)) and A(1)(TO(2)) modes, the half-width composition and the area ratio of the A(1)(TO(4)) and E(TO(8)) bands, we reached several conclusions about the incorporation mechanism of the Nd and Mg ions into the LiNbO(3) lattice. Likewise the Raman shift and half-width of the E(TO(1)) and E(TO(7)) modes were investigated in the Z direction. Results indicate that Mg and Nd ions are located in the Li site for low doping concentrations and for larger concentrations there is a replacement in both Li and Nb ion sites.

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Large-area, flexible, two-dimensional transition metal dichalcogenide semiconductor materials (MoS2 and WSe2) were synthesized via magnetron sputtering of amorphous stoichiometric precursor materials on polydimethylsiloxane polymer substrates. Purely amorphous precursor materials and amorphous materials with pre-existing nanocrystalline regions observed via transmission electron microscopy were grown for the studies presented here. The MoS2 and WSe2 material precursors were then illuminated with a pulsed 532 nm laser to induce crystallization to their semiconducting hexagonal phases. The laser optics included an axicon lens to shape the Gaussian pulsed laser into a “Bessel beam” characterized by annular ring geometry. The pattern of the beam, with its rings of high-intensity laser light around a higher-intensity core, produced crystalline rings of the material around an ablation zone on the polymer substrate for MoS2 and WSe2 materials. The crystalline structure and density of atomic defects over the crystalline regions decreased as the same sample area was illuminated with additional pulses. The lateral coherence of the crystal lattice increased with the first 4 pulses but decreased with each subsequent pulse. The impact of preexisting nanocrystalline nanoinclusions in an amorphous film on the crystallization rate for WSe2 precursor materials was examined. The presence of nanocrystalline regions in the amorphous materials increased the crystallization rate under the photonic annealing conditions examined here. This approach of direct synthesis and patterning of materials is a route toward the fabrication of inexpensive flexible electronic devices.

The foremost advanced photoacoustic (PA) transport theory, dealing with image formation, relates to target volumes of shallow depths. It assumes the medium as homogeneous with negligible PA amplitude attenuation. Causal changes in the velocity distribution spectrum, as described in Debye’s theory, and related to propagation distance and sample's density, are also neglected. However, these are relevant for imaging targets at larger depths and improving image resolution of PA images of thick biological tissues. Here we introduce some concepts for extending the PA transport model. These are theoretical and experimental considerations for analysing PA attenuation and the significance of spectral dispersion; and in consequence, disclose those conditions at which they should be included as part of the PA transport theory. Departing from the PA Heaviside telegraph equation and causality conditions, we obtain analytic expressions for associated attenuation and dispersion coefficients. As part of the analysis, we propose expressions for the PA group and PA phase velocities, and for the group velocity dispersion parameter; those in analogy with optical fields. In this way we get a refined description for the spectral dispersion. As proof of consistency, the introduced expressions are tested with experimental data extracted from homogeneous colloid samples. The observed performance is compared against already known general acoustic dispersion theory.

BACKGROUND Endoscopic ultrasound (EUS) and endoscopic ultrasound elastography (EUS-E) simulation lessens the learning curve; however, models lack realism, diminishing competitiveness. AIM To standardize the mechanical properties of polyvinyl alcohol (PVA) hydrogel for simulating organs and digestive lesions. METHODS PVA hydrogel (Sigma Aldrich, degree of hydrolysis 99%) for simulating EUS/EUS-E lesions was investigated in Unidad de Investigación y Desarrollo Tecnológico at Hospital General de México “Dr. Eduardo Liceaga”, Mexico City. We evaluated physical, contrast, elasticity and deformation coefficient characteristics in lesions, applying Kappa’s concordance and satisfaction questionnaire (Likert 4-points). RESULTS PVA hydrogel showed stable mechanical properties. Density depended on molecular weight (MW) and concentration (C). PVA bblocks with the greatest density showed lowest tensile strength ( r = -0.8, P = 0.01). Lesions were EUS-graphically visible. Homogeneous and heterogeneous examples were created from PVA blocks or PVA phantoms, exceeding (MW 2 = 146000-186000, C 9 = 15% and C 10 = 20%) with a density under (MW 1 = 85000-124000, C 1 = 7% and C 2 = 9%). We calculated elasticity and deformation parameters of solid (blue) areas, contrasting with the norm (Kappa = 0.8; high degree of satisfaction). CONCLUSION PVA hydrogels were appropriate for simulating organs and digestive lesions using EUS/EUS-E, facilitating practice and reducing risk. Repetition amplified skills, while reducing the learning curve.