Good dielectric performance and broadband dielectric polarization in Ag,Nb co-doped TiO2

Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO₂-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag⁺/Nb⁵⁺ co-doped (Ag_1/4Nb_3/4)_xTi_1−xO₂ (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 10³ and 1.6 × 10⁴ at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics.     

温度对变压器绝缘缺陷影响规律的分析及验证

本文中作者研究了温度对油浸式变压器绝缘纸老化水平的影响,开展了频域介电谱测试得出不同的试验温度下绝缘纸的电导率频域谱.推导了温度、电导率和相对介电常数之间的作用情况,并进行实例验证.     

VO2/GaAs异质结的制备及其光电特性研究

采用直流磁控溅射和后退火氧化工艺在p型GaAs单晶衬底上成功制备了n-VO_2/pGaAs异质结,研究了不同退火温度和退火时间对VO_2/GaAs异质结性能的影响,并分析其结晶取向、化学组分、膜层质量以及光电特性。结果表明,在退火时间2 h和退火温度693 K下能得到相变性能最佳的VO_2薄膜,相变前后电阻变化约2个数量级。VO_2/GaAs异质结在308 K、318 K和328 K温度下具有较好的整流特性,对应温度下的阈值跳变电压分别为6.9 V、6.6 V和6.2 V,该结果为基于VO_2相变特性的异质结光电器件的设计与应用提供了可行性。     

Comparison of yield and metabolites according to the types of hilling materials utilized during Glehnia littoralis sprout vegetable cultivation

Food Science and Biotechnology - Various hilling materials (rice hulls, pine sawdust, and perlite) were compared to produce sprout vegetables using beach silvertop (Glehnia littoralis Fr. Schm. ex...     

TEMPO氧化修饰的天然多糖纳米纤维增强复合材料及其功能化研究进展

纤维素和几丁质具有相似的结构，是自然界中储量丰富的两类天然多糖。经2, 2, 6, 6-四甲基哌啶氮氧化物(TEMPO)氧化修饰制备的纤维素和几丁质纳米纤维，不仅具有多糖类物质的良好亲水性、生物可降解性、生物相容性及丰富的官能团(羟基、羧基、乙酰氨基和氨基等)所带来的特定化学性质，而且还具有纳米纤维的纳米尺寸效应、大比表面积、高表面活性、高结晶度和手性液晶相结构等特点，已成为生物质纳米材料领域的研究重点之一。本文对TEMPO氧化修饰制备天然多糖纳米纤维的方法及剥离机制进行了总结，同时重点综述了TEMPO氧化修饰的天然多糖纳米纤维在薄膜、凝胶、导电、医用、电磁屏蔽及环境等复合材料的增强和功能升级等方面的研究进展，强调了纤维素和几丁质纳米纤维的官能团及纳米尺寸在复合材料中的增效机制。最后，对天然多糖纳米纤维的发展方向及其在各领域应用的机遇与挑战进行了展望。     

承插型盘扣式支撑架在地铁车辆段工程中的应用

盘扣式支撑架具有承载力强、方便安全、结实耐用等优点,被广泛应用于地铁施工。本文以广州市轨道交通十八号线万顷沙车辆段为例,对承插型盘扣式支撑架在地铁车辆段工程中的具体应用进行了详细说明,以期为同类工程提供参考。     

Ensemble relation network with multi-level measure

Fine-grained few-shot learning is a difficult task in image classification. The reason is that the discriminative features of fine-grained images are often located in local areas of the image, while most of the existing few-shotlearning image classification methods only use top-level features and adopt a single measure. In that way, the localfeatures of the sample cannot be learned well. In response to this problem, ensemble relation network with multi-level measure (ERN-MM) is proposed in this paper. It adds the relation modules in the shallow feature space tocompare the similarity between the samples in the local features, and finally integrates the similarity scores from thefeature spaces to assign the label of the query samples. So the proposed method ERN-MM can use local details andglobal information of different grains. Experimental results on different fine-grained datasets show that the proposedmethod achieves good classification performance and also proves its rationality.     

Effect of wind condition on unintended hydrogen release in a hydrogen refueling station

Ambient condition, especially the wind condition, is an important factor to determine the behavior of hydrogen diffusion during hydrogen release. However, only few studies aim at the quantitative study of the hydrogen diffusion in a wind-exist condition. And very little researches aiming at the variable wind condition have been done. In this paper, the hydrogen diffusion in different wind condition which including the constant wind velocity and the variable wind velocity is investigated numerically. When considering the variable wind velocity, the UDF (user defined function) is compiled. Characteristics of the FGC (flammable gas cloud) and the HMF (hydrogen mass fraction) are analyzed in different wind condition and comparisons are made with the no-wind condition. Results indicate that the constant wind velocity and the variable wind velocity have totally different effect for the determination of hydrogen diffusion. Comparisons between the constant wind velocity and the variable wind velocity indicate that the variable wind velocity may cause a more dangerous situation since there has a larger FGC volume. More importantly, the wind condition has a non-negligible effect when considering the HMF along the radial direction. As the wind velocity increases, the distribution of the HMF along the radial direction is not Gaussian anymore when the distance between the release hole and the observation line exceeds to a critical value. This work can be a supplement of the research on the hydrogen release and diffusion and a valuable reference for the researchers.     

消防战勤保障体系建设的思考

随着经济的发展,消防救援队伍承担的任务越来越繁重.重大灾害事故的发生,对消防战勤保障方面提出了更高的要求.文章主要从消防战勤保障的主要任务职能、消防战勤的任务分类以及消防战勤保障体系建设存在的问题与建议等几个方面进行了详细的阐述,以期消防战勤保障得到更好的发展.