In view of thermal resistance problem of the motorized spindle system, this paper proposes a thermal resistance network model of spindle-bearing-bearing pedestal based on the fractal and Hertz contact theory. According to this model and Kirchhoff's law, the heat balance equations for thermal nodes are established and solved with Gauss-Seidel iterative method to gain temperature values of the main thermal nodes. In order to accurately understand thermal characteristics of the motorized spindle system, the effect of thermal contact resistance and thermal-conduction resistance is taken into consideration. Thermal simulation analysis is carried out on the motorized spindle system. On a precision horizontal machining center, the temperature rise of motorized spindle parts is implemented under different rotational speeds with LMS data acquisition system. It is shown that temperature values based on thermal resistance network model agree well with those of simulation analysis and experimental results. What is more, the whole thermal deformations of the main components of the motorized spindle system are analyzed.
AgNbO3-based lead-free ceramics are a promising candidate material for capacitors, where thermal stability is a key property for applications in severe and complex environments. This study investigated the fabrication of Ag1-3xBixNb1-3/5x(Zn1/2Ti1/2)xO3
(ABNZT-x) (x = 0, 0.005, 0.01, 0.02, or 0.04) via a solid-state reaction under oxygen flow. The microstructure, dielectric properties, and impedance spectra of the AgNbO3 samples co-doped with Bi3+, Zn2+, and Ti4+ were systematically
characterized. All samples exhibited an orthorhombic phase structure, where the average grain size decreased with increasing co-doping level, the grain growth kinetics was studied by phase-field simulation. The phase transition temperatures became lower and the maximum permittivity values
decreased. These findings demonstrated that enhanced dielectric thermal stability had been achieved. The grain conduction effect was observed during the impedance spectroscopy analysis, where the calculated activation energy decreased with increasing co-doping level. This ABNZT-x ceramic
system exhibited stable dielectric properties, and shows promise for use as a functional material in electronic devices.
The multi-cusped field thruster is a kind of electric thruster adopting a cusped magnetic field to achieve a potentially longer lifetime. It is observed in some experiments that the main electric potential drop forms near the exhaust plane, but the formation mechanism of the electric field in this kind of thrusters is not fully clear yet. Based on the analysis of the electron movement, a 2D Particle-in-Cell plus Monte Carlo model is built to reveal the difference of the constraint to electrons between the central leak path and the lateral region of the thruster. Electron trajectories from cathode are analyzed furthermore. It is found that the central leak path inside the discharge channel may play a significant role in the formation of the main electric potential drop near the exhaust plane.
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