Solid Polymer Electrolytes from Copolymers Based on Vinyl Dimethyl Phosphonate and Vinylidene Fluoride

Solid polymer electrolytes are prepared by mixing various amounts of lithium bis(trifluoromethanesulfonyl)imide with poly(vinylidene fluoride‐co‐vinyl dimethyl phosphonate) statistical copolymers with different compositions. Such copolymers are obtained by conventional radical copolymerization of vinylidene fluoride (VDF) with vinyl dimethyl phosphonate (VDMP) initiated by peroxides. A morphological study of the obtained solid polymer electrolytes (SPEs) shows that only samples prepared from the copolymer with the lower amount of VDMP (16 mol%) result in the formation of homogeneous electrolytes while aggregates of lithium salts are observed for the other copolymers. The best ionic conductivity values are accordingly observed for the copolymers with the lower VDMP amount and are reaching 5 × 10^?3 mS cm^?1 at 100 °C. The dependence of the ionic conductivity versus temperature suggests that the ionic conductivity is controlled by the motion of polymer segments. Indeed, the ionic conductivity can be increased by adding a small amount of trimethylphosphate plasticizer and can reach 1.9 × 10^?2 mS cm^?1 at 20 °C. Finally, the prepared SPEs exhibit a high electrochemical stability and a good resistance to flame because of the presence of fire‐retardant phosphate groups in their structure.     

Comparison of the effect and safety of Er:YAG laser combined with fluoride and methylene blue-photodynamic therapy on caries prevention

目的 比较Er:YAG激光-氟化钠联合法与亚甲基蓝-光动力疗法（MB-PDT）的防龋效果及安全性。方法 建立28只大鼠龋齿模型,随机分成7组：不同功率密度的光动力疗法（PDT）组、激光+氟化钠联合组、激光组、氟化钠组和0.9%生理盐水组。分光光度法检测变异链球菌生长抑制情况;激光荧光诊断仪（LF）检测龋损脱矿程度;组织病理观察牙髓及颊黏膜损伤状况。结果 PDT组与激光+氟化钠联合组光密度值明显低于其他处理组（P<0.05）;不同处理方法均可使LF值上升,出现不同程度的脱矿;组织病理学观察,70 mw·cm^-2的联合组和Er:YAG激光组存在牙髓及颊黏膜损伤。结论 相同参数下,联合组与PDT均有良好的杀菌效果,但PDT不良反应少、损伤小,是一种高效且安全的防龋手段。     

含氟涂漆与CPP-ACP或生物活性玻璃对根龋的作用评价

目的：体外研究含氟涂漆与酪蛋白磷酸肽-非结晶型磷酸钙(casein phosphopeptide-amorphous calcium phosphate,CPP-ACP)或生物玻璃对根龋的作用。方法：选择2017年4月—2018年10月北京大学人民医院口腔科收集的84颗活动性根龋牙,随机分为A、B、C、D组,每组均21颗牙,4组均给予含氟牙膏刷牙,B组增加含5%氟化钠的涂漆,C组增加含5%氟化钠+CPP-ACP的涂漆,D组增加含5%氟化钠+生物活性玻璃的涂漆。观察涂漆前、后各组根龋严重程度、表面粗糙度、矿物质浓度。采用SPSS 23.0软件包分析根龋严重程度与表面粗糙度的相关性。结果：B、C、D组涂漆50 d后硬度显著高于涂漆前及A组（P<0.05）;C、D组涂漆50 d后硬度显著高于B组（P<0.05）;D组涂漆50 d后硬度显著高于C组（P<0.05）。涂漆7 d后,B、C组表面粗糙度评分均显著高于A、D组（P<0.05）;涂漆14 d后,B组表面粗糙度评分均显著高于A、C、D组（P<0.05）;涂漆50 d后,D组表面粗糙度评分显著高于B、C组（P<0.05）。A组根龋严重程度评分与表面粗糙度呈负相关（P<0.05）。各组涂漆50 d后矿物质浓度均显著高于涂漆前（P<0.05）。结论：含氟化物+CPP-ACP或生物活性玻璃涂漆均具有显著阻止根龋的作用,生物活性玻璃较CPP-ACP更稳定,提高牙表面矿物质浓度效果更好。     

Determination of Impact Damage in CFRP via PVDF Signal Analysis with Support Vector Machine

Carbon fiber reinforced plastics (CFRPs) have high specific stiffness and strength, but they are vulnerable to transverse loading, especially low-velocity impact loadings. The impact damage may cause serious strength reduction in CFRP structure, but the damage in a CFRP is mainly internal and microscopic, that it is barely visible. Therefore, this study proposes a method of determining impact damage in CFRP via poly(vinylidene fluoride) (PVDF) sensor, which is convenient and has high mechanical and electrical performance. In total, 114 drop impact tests were performed to investigate on impact responses and PVDF signals due to impacts. The test results were analyzed to determine the damage of specimens and signal features, which are relevant to failure mechanisms were extracted from PVDF signals by means of discrete wavelet transform (DWT). Support vector machine (SVM) was used for optimal classification of damage state, and the model using radial basis function (RBF) kernel showed the best performance. The model was validated through a 4-fold cross-validation, and the accuracy was reported to be 92.30%. In conclusion, impact damage in CFRP structures can be effectively determined using the spectral analysis and the machine learning-based classification on PVDF signals.