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The time-resolved fluorescence of p-terphenyl, 2,2″-dimethyl-p-terphenyl (dm-terphenyl), and tetracene dissolved in solvents was measured with fluorescence up-conversion and time-correlated single-photon counting. We characterized the relaxation dynamics of vibrational energy in these three molecules by examining their properties in solvents of varied physical properties. According to the measured curves of fluorescence decays obtained at excitation wavelength 266/256 nm, we propose that p-terphenyl and dm-terphenyl both undergo initially an ultrafast intramolecular redistribution of vibrational energy. A conformational relaxation of p-terphenyl in excited-state S 1 with time constant 6–13 ps is proposed from its linear dependence on the viscosity of solvents. This process and vibrational energy relaxation are accelerated in a protic solvent involving efficient coupling to the high-energy bath modes of the solvent. Because the torsional conformational change of dm-terphenyl is effectively inhibited by the steric hindrance imposed by its methyl substituents, its vibrational relaxation is found to be independent of the viscosity of the solvent but remains rapid with time constant 5.2–8.8 ps. The time constant of vibrational relaxation in tetracene is observed to be 12–16 ps, with no evident dependence on solvent viscosity or thermal diffusivity. The fact that accepting modes with greater energy are more effective in transferring energy for a system with a large excess of vibrational energy is proposed to explain the ratio of the rates of vibrational relaxation for methanol MeOH/MeOD ≈ 2.

Center of pressure (COP) during a gait cycle indicates crucial information with regard to fall risk such as balance capacity. The drawbacks of conventional research instruments include inconvenient use during activities of daily living and expensive costs. The present study illustrates the promising fall-relevant information predicted by acceleration and angular velocity data from different placement sensors with machine learning techniques. This approach is inspired by the emerging machine learning technique, specifically the long short-term memory (LSTM), which is often used in time series data and aims to decrease the burden of the user while using the novel wearable technology. The Jaccard similarity coefficient, which implies the consistency of profile alignment between prediction and real situation, achieved 94% accuracy in the walking direction. Furthermore, the number of sensors used and the placement influenced the feasibility of an application. The outcome revealed that the accuracy could exceed 90% with only one sensor placed on the foot in the walking direction, and the toe would be the best location for sensor placement. To examine the performance of machine learning, the current study employed two parameters from different perspectives. One is a commonly used parameter, which represented the error, and the other investigated the similarity between the prediction and ground truth. From a similarity perspective, the parameter can be used as a metric to assess the consistency of profile alignment.

The relaxation dynamics of the excited states of stilbene 3 in various solvents, confined environment cetyltrimethylammonium bromide (CTAB) micelle, and water/bis(2-ethylhexyl) sulfosuccinate (AOT)/hexane reverse micelle are investigated. In the time-resolved decay curves of fluorescence measured in solution at excitation wavelength 256 or 266 nm, stilbene 3 underwent initially an ultrafast internal conversion to the S2 state or was directly excited at the S2 then via a conformational relaxation with time constant 1.1-4.6 ps. This relaxation process displays a linear dependence on solvent viscosity. Slow relaxation in deuterated methanol and water is explained that the vibrational energy is efficiently coupled to the librational modes of solvent. The conformational relaxation rate decreases slightly in the CTAB micelle but is greatly hindered in the AOT reverse micelle with small cavities. According to the results of anisotropy measurements, in both CTAB and AOT reverse micelles with a cavity diameter as large as ∼7 nm, the dynamics of molecular rotation remain significantly hindered.