Colloidal nanoparticles: Mechanisms of laser synthesis and interactions
Laser ablation in liquids is now commonly used to produce colloidal nanoparticles (NPs) that have found numerous applications in different areas. In the experiments, NPs of different materials can be rather easily produced by using laser systems with various pulse durations, shape, wavelengths, and fluence. Here, we focus our attention on metal nanoparticles produced by ultra-short laser pulses.
Modeling nanoparticle formation by laser ablation and by spark discharges
Nanoparticles have found numerous applications in such areas as photonics, electronics, medicine, etc. Further development of these fields requires reliable and versatile methods of nanoparticle synthesis with well-controlled properties. Among promising synthesis techniques, both laser ablation and plasma discharges are considered. These methods provide numerous advantages that are unique in several cases. On one hand, the main advantage of the laser ablation method is in the possibilities of changing laser parameters and background conditions and in its capacity to preserve stoichiometry. Laser-based methods also yield bio-compatible nanoparticles and nano-colloids with unique chemical properties. Laser-induced fragmentation provides additional control ways over nanoparticle sizes. To better understand and to optimize these processes, detailed numerical modeling is performed. The involved stages are considered and analyzed. The resulting nanoparticle parameters are investigated as a function of the experimental conditions. Nanoparticle properties, such as mean size and mean concentration are analyzed. Differences and similarities between the considered synthesis methods are discussed.
Transient nonlinear thermal stability analysis of metro cable under pulse power
The load of metro cable system varies a lot from morning rush hours to the evening closure time. With many trains hopping in the rush hours, the long term and economical short term thermal stability become a big issue as a result of the large difference between thermal time constant and the electrical time constant of cable. Based on a 10kV three-core XLPE metro power cable model, the theoretical thermal capacity was calculated according IEC standard. Then, a Finite Element Method (FEM) was employed to analyze the transient electro-thermal phenomena, taking into account various types of power loss in cable system and the non-linear electrical conductivity of the conductor. Finally, the thermal distribution inside the cable was presented as a function of time, and the maximum thermal capacity was predicted in metro cable.