Vibrational energy distribution in plate excited with random white noise

In Statistical Energy Analysis (SEA) and more generally in all statistical theories of sound and vibration, the establishment of diffuse field in subsystems is one of the most important assumption. Diffuse field is a special state of vibration for which the vibrational energy is homogeneously and isotropically distributed. For subsystems excited with a random white noise, the vibration tends to become diffuse when the number of modes is large and the damping sufficiently light. However even under these conditions, the so-called coherent backscattering enhancement (CBE) observed for certain symmetric subsystems may impede diffusivity. In this study, CBE is observed numerically and experimentally for various geometries of subsystem. Also, it is shown that asymmetric boundary conditions leads to reduce or even vanish the CBE. Theoretical and numerical simulations with the ray tracing method are provided to support the discussion.

Динамика термолюминесценции при двойном лазерном Vis-IR возбуждении молекул эозина с кислородом и наночастицами серебра в пленке поливинилбутираля

Electronic and vibrational energy transfer processes taking place in molecular complexes in a polymer are investigated under dual-wavelength (visible at λ = 532 nm and IR at wavelength λ = 10.6 μm) laser photoexcitation of eosin molecules ( С = 4 × 10^–4 М) in air and without it ( р ≈ 10^–4 Torr) in thin polyvinyl butyral (PVB) films containing silver nanoparticles ( R ≈ 36 nm) prepared by laser ablation. Generation of singlet oxygen, singlet–triplet annihilation, and enhancement of plasmon quenching of dye fluorescence are studied. Thermal-energy transfer processes in thin PVB films following pulsed IR excitation are simulated, and the temperature conductivity coefficients of the polymer films in the presence of silver nanoparticles are calculated. Low-temperature processes in PVB films containing dye molecules taking place after IR excitation are investigated, and the mechanism for accelerating intercombination S _1 → Т _1 transitions as a result of thermal heating and intramolecular vibrational-energy distribution is explained.