ABSTRACT
In this study, a flexible wheelset was added to a rigid-flexible coupled vehicle dynamics model, in which the axle box bearings are accurately modeled. The measured wheel's polygon wear profile and Wuhan-Guangzhou track spectrum are used in the model to define the wheel tread and track irregularity, respectively. We conducted a field test on the Wuhan-Guangzhou railway line to validate the model. Then, we investigate how the dynamic properties of the axle box bearing are impacted by the wheelset flexibility and polygonal wear of wheel. We found that the polygonal wheel with a rigid wheelset causes high-frequency vibration in wheelset and axle box, and increases the axle box bearing's internal contact force. Additionally, the flexible wheelset with a normal wheel tread can alleviate the wheel/rail impact and reduce the axle box's vertical vibration as well as the axle box bearing's internal contact force. When the vehicle is running at v = 300 km/h, the excitation frequency caused by the wheel's 20th-order polygon is 576.5 Hz, and the flexible wheelset's 20th-order modal frequency is 577 Hz. The two frequencies are similar, when considering the polygonal wheel and flexible wheelset simultaneously, the wheelset will resonate. And the resonate of wheelset will increase the local deformation of the axle end and deteriorate the bearing operating environment, causing a significant increase in the bearing contact force. Finally, the axle box bearing's dynamic characteristics are summarized when vehicle velocity varies from 50 to 350 km/h and wheel polygon wear amplitude ranges from 0.01 to 0.05 mm.
ABSTRACT
Real-time monitoring of singlet-triplet transitions is an effective tool for studying room-temperature phosphorescent molecules. For femtosecond transient absorption (TA) spectroscopy of a 2,6-di(9H-carbazol-9-yl) pyridine molecule in dimethyl sulfoxide (DMSO), the stimulated emission signal (380 nm) and the excited-state absorption signal (650 nm) reach their maximum intensity within 397 fs. Subsequently, the two signals decay with time and the triplet-triplet absorption (TTA) signal (400 nm) is enhanced synchronously, accompanied by an isosbestic point at 491 nm. These results confirm intersystem crossing (ISC) within 2.5 ns. Moreover, the TTA signal (400 nm) in nanosecond TA spectroscopy gradually disappeared, accompanied by a phosphorescence lifetime of 4.1 µs. As the solvent polarity decreases (DMSO > N,N-dimethylformamide > 1,4-dioxane > toluene), similar spectral dynamic processes are observed, while the durations of ISC processes and phosphorescence lifetimes are shortened. This combined femtosecond and nanosecond transient absorption spectroscopy study presents the ultrafast excited-state dynamics of organic phosphorescent molecules.
ABSTRACT
A new action mechanism for the fluorescent detection on the Al3+ ion of the sensitive 1-((2-hydroxynaphthalen-1-yl)methylene)urea(OCN) is theoretically studied. The extensive theoretical calculations on the OCN and the isomer structure OCN-T are performed. The emission and absorption spectra consistent with the experiment value. The absorption spectra peaks (362 nm and 326 nm) of OCN and OCN-T molecules are attributed to the experimentally observed absorption spectra at 356 nm and 314 nm, respectively. The calculated fluorescence value of the OCN-AL structure is 460 nm, while the OCN-T-AL structure has no fluorescence. These results better explain that OCN and its isomers OCN-T are involved in the absorption, and the detection spectrum signal is emitted from the OCN-AL complex. The OCN and OCN-T molecules are obvious hydrogen bonding systems. The excited state intramolecular proton transfer photochemical behaviors and detecting Al3+ ion photophysical changes were explained for the first time at the molecular level. As driving force of excited state intramolecular proton transfer (ESIPT) reaction, the bond parameters and vibrational frequencies of intramolecular hydrogen bond were analyzed by optimizing structures and calculating infrared spectra, analysis of frontier molecular orbitals. To further elucidate the proton transfer reactive paths, the scanned the potential energy curves (PECs) of OCN and OCN-T chemosensor in different electronic states are plotted. This work proposes a reasonable explanation for the detection mechanism of the OCN sensor.
