超临界CO2萃取茶叶籽油及其分子蒸馏馏出物抗氧化成分分析

以茶叶籽为原料,采用超临界CO2萃取得到茶叶籽油,通过分子蒸馏富集提取茶叶籽油中抗氧化成分,并采用UHPLC-TOF-MS分析其组成。结果表明,CO2流速对萃取速率影响较大,采用超临界CO2梯度萃取的模式,不同萃取阶段得到的茶叶籽油的酸价存在一定规律,在萃取初期,茶叶籽油的酸价较高,随着萃取过程的进行,酸价逐渐降低,说明游离脂肪酸更容易溶解在超临界CO2中。茶叶籽油分子蒸馏馏出物中主要的抗氧化成分包括：山茶甙C,表儿茶素没食子酸酯,表阿福豆素,表儿茶素及表没食子儿茶素等5种。     

Students' mental load,stress, and performance when working with symbolic or symbolic–textual molecular representations

In science education, representations are necessary inter alia for the understanding of relationships between structures and systems. However, several studies have identified difficulties of students when working with representations. In the present study, we investigated students' responses (regarding their preference, test performance, mental load (ML), and stress) toward two kinds of representations: symbolic representations, which only use abstract symbols, versus combined symbolic–textual representations, which additionally comprise textual elements. Therefore, students were randomly assigned to one of two treatment groups: one group worked on test tasks accompanied by symbolic representations, and the others worked on the same tasks, but with symbolic–textual representations. Thereafter, the students' test performance and ML were assessed. The level of perceived stress and the salivary cortisol concentration were measured before and after the test and again a few minutes later. Additionally, heart rate variability parameters were assessed continuously. We found a strong preference of the test version with symbolic representations. Additionally, the students showed better test performance and lower ML when they worked with symbolic representations. However, the level of perceived stress was comparable between both groups and there was no strong physiological stress response: The cortisol concentration decreased in both groups and the heart rate was relatively similar. However, during the second half of the test, we observed a significantly higher ratio between low and high heartbeat frequencies in the group with symbolic–textual representations and we found an indirect influence of the kind of representation on test performance through its effect on ML. The poorer test performance and higher ML in connection with symbolic–textual representations confirm previous studies, which found that symbolic–textual representations pose major problems for students. Thus, teachers should enable students to understand symbolic–textual representations and consider carefully whether they can use symbolic representations instead, especially when they teach complex content.     

基于TKX-50的PBXs含能材料力学性能计算模拟

在含能材料中添加高分子粘结剂来制备高聚物粘结炸药(PBXs)是改善其力学性能的一种重要手段.含能材料1,1'-二羟基-5,5'-联四唑二羟胺盐(TKX-50)具有高储能、高爆速、低灵敏度和低毒性等特点.将TKX-50分别与HMX和RDX混合得到TKX-50/HMX混合体系和TKX-50/RDX混合体系.该文利用分子动力...     

Comparing the effectiveness of video and stereoscopic 360° virtual reality-supported instruction in high school biology courses

The promise of using immersive technologies in learning has increasingly been attracting researchers' and practitioners' attention. However, relevant empirical works are usually conducted in fully controlled Virtual Reality (VR) laboratories, as opposed to conventional settings. This quasi-experimental study compares the effectiveness of video learning resources to that of stereoscopic 360° VR, as supplements to the traditional instructional approach. The potential of such methods was examined in high school settings, in the context of the ‘Life and Evolution’ module, with participants (n = 70) divided equally into control and experimental groups. As a point of reference (control condition), we considered the adoption of Video Learning Resources, as students are more acquainted with this instructional method. In the intervention approach (experimental condition), students adopted the use of low-end mobile-VR (VeeR Mini VR Goggles). The key findings indicate differences in the learning motivation, confidence and satisfaction, but no statistically significant difference was identified regarding the factual or conceptual knowledge gains. The study offers insights on the potential of the investigated technologies in the subject of secondary school Biology and further provides implications for theory and practice.

Practitioner notes

What is already known about this topic

• Researchers' interest over the potential of Virtual Reality on different STEM disciplines is increasing consistently.
• An increasing number of efforts can be identified discussing the integration of multimedia learning resources in the secondary school context.
• Empirical studies on the subject of Biology are focusing on students' academic performance and achievement but not on learning motivation and satisfaction.

What this paper adds

• This quasi-experimental study comparatively examines academic performance, with the focus being on learning motivation and satisfaction, across different modalities (stereoscopic 360° Virtual Reality applications-VR, Video Learning Recourses-VLR).
• The findings demonstrate that both instructional methods are sufficient in enhancing students' knowledge acquisition and academic performance.
• The adoption of stereoscopic 360° VR influences students' learning motivation and impacts long-term memory retention.

Implications for practice and policy

• Educators are advised to consider the systematic adoption of “immersive” multimedia tools to enhance the subject of Biology as they can greatly encourage scientific inquiry.
• Instructional designers are advised to adopt open educational resources aligned to the curriculum of the local context.
• Educational researchers are advised to integrate stereoscopic 360°-VR solutions in the conventional classroom settings.