ABSTRACT
Polymer dielectrics are highly desirable in capacitor applications due to their low cost, high breakdown strength, and unique self-healing capability. However, existing polymer dielectrics suffer from either a low energy density or a high dielectric loss, thereby hindering the development of compact, efficient, and reliable power electronics. Here, a novel type of polymer dielectrics simultaneously exhibiting an extraordinarily high recoverable energy density of 35 J cm-3 and a low dielectric loss is reported. It is synthesized by grafting zwitterions onto the short side chains of a poly(4-methyl-1-pentene) (PMP)-based copolymer, which increases its dielectric constant from ≈2.2 to ≈5.2 and significantly enhances its breakdown strength from ≈700 MV m-1 to ≈1300 MV m-1 while maintaining its low dielectric loss of <0.002 and high charge-discharge efficiency of >90%. Based on a combination of the phase-field method description of mesoscale structures, Maxwell equations, and theoretical analysis, it is demonstrated that the outstanding combination of high energy density and low dielectric loss of zwitterions-grafted copolymers is attributed to the covalent-bonding restricted ion polarization and the strong charge trapping by the zwitterions. This work represents a new strategy in polymer dielectrics for achieving simultaneous high energy density and low dielectric loss.
ABSTRACT
Extremely high temperature in a chip will severely affect the normal operation of electronic equipment; however, the traditional air conditioning cooling technology is unsuitable for integrated circuit cooling. It is necessary to develop convenient and high-efficiency cooling techniques. In this paper, PbHfO3 antiferroelectric (PHO AFE) film was fabricated by a sol-gel method and was first found to be a promising electrocaloric (EC) material with high temperature change (ΔT â¼ -7.7 K) and acceptable EC strength (|ΔT/ΔE| â¼ 0.023 K cm kV-1) at room temperature. In addition to the negative EC effect (ECE), a large positive ECE can be observed at high temperature. The outstanding ECEs and their combination will make the PHO film one of the potential candidates for next-generation solid-state refrigeration. To understand the underlying physical mechanism for positive and negative ECEs in the PHO AFE film, a modified Ginzburg-Landau-Devonshire free-energy theory is adopted.
ABSTRACT
PURPOSE: To investigate the changes in vault and the effect on visual outcomes 1 year after implantable Collamer lens (ICL) implantation. METHODS: In this retrospective study, 127 eyes of 66 patients undergoing ICL implantation were examined both before and up to 1 year after the surgery. The examination contents included white-to-white (WTW) diameter, central vault of the ICL (distance between posterior surface of ICL and anterior surface of crystalline lens), refractive error, and wavefront high-order aberration (HOA). All statistical analyses were performed using SPSS 13.0 software. RESULTS: A significant decrease in vault was noted up to 1 month, after which the value stabilized (p=0.001). The moderate vault decreased significantly after the first 3 months postsurgery (paired-samples t test, p<0.05). Low vault showed a tendency to increase and high vault showed a tendency to decrease, but not significantly, over time. There was no statistically significant correlation between the amount of vault and the refractive error (Pearson correlation coefficient R=0.111, p=0.473) and there was a statistically significant correlation between the vault and HOAs (R=0.304, p=0.024). CONCLUSIONS: Implantable Collamer lens vault over the crystalline lens had the tendency toward a slight decrease with time and did not significantly affect the vision outcome 1 year after surgery.
