Ceramic capacitors with upper operating temperatures far beyond 200°C are essential for high-temperature electronics used in deep oil drilling, aviation, automotive industry and so on. Recent advances in existing lead-free dielectrics for potential high-temperature capacitor applications are reviewed and grouped into three categories according to the parent component of the solid solution. Their desirable temperature stabilities were summarised comprehensively. However, there are still some limitations in the current research, such as achieving low loss in a wide temperature range and maintaining stable dielectric properties with different frequencies or at different voltages. Furthermore, the successful implementation of multilayer ceramic capacitors is one of the biggest challenges, which will have far-reaching impacts on the realisation of high-temperature capacitor application in the future.

An ultra-wide temperature stable ceramic system based on (1Àx) [0.94 (0.75Bi 0.5 Na 0.5 TiO 3 À0.25NaNbO 3 )À0.06BaTiO 3 ]ÀxCaZrO 3 (CZ100x) is developed for capacitor application in this study. All samples exhibit characteristics of pseudocubic structures in XRD patterns. With CaZrO 3 addition, the coupling effect of polar nanoregions (PNRs) is weakening, leading to greatly improved temperature stability of dielectric properties. Among all samples, the most attractive properties are obtained in the composition of CZ10 at <15% variation in dielectric permittivity spanning from À55°C to 400°C and lower than 0.02 of dielectric loss of between À60°C and 300°C, accompanied by high DC resistivity (10 7 Ω m at 300°C, calculated by fitting Jonscher's power law). Furthermore, tentative multilayer ceramic capacitors (MLCCs) composed of CZ10 dielectric and Ag:Pd (70:30) internal electrode layers were fabricated by tape casting and cofiring processes. Temperature-stable dielectric property in formation of MLCC was successfully realized, with small DC/C 25°C (<15%) and loss factor (≤ 0.02) between À55°C and 340°C. Meanwhile, CZ10-based MLCC showed temperatureinsensitive energy storage density of 0.31À0.35 J/cm 3 and high-energy efficiency of above 77% at 120 kV/cm in the range of À55 to 175°C. All of these exhibit wonderful temperature-stable dielectric properties and indicate the promising future of CZ10 dielectric as high-temperature ceramic capacitors. K E Y W O R D Scapacitor, ultra-high temperature ceramics, dielectric materials/properties

No abstract

No abstract

As a key problem of cloud computing, the performance of task scheduling strategy may seriously affect the efficiency and service quality of the system. With the purpose of achieving balanced task scheduling with optimal completion time, ant colony optimization (ACO) algorithm is adopted as task scheduling strategy in this paper. Considering the problem of premature convergence to local optimal solution of ACO, an improved Max-Min Ant System (MMAS) is introduced to find the global optimal solution. Based on the study of pheromone’s updating mechanism of MMAS, MMAS is applied as task scheduling strategy with reasonable mapping from the objective of shortest path to shortest completion time. The task scheduling strategy based on MMAS has been simulated from views of tasks’ number, size and load balance, and the results shows that MMAS task scheduling strategy is with a better performance on completion time and load balance than ACO based strategy.?