12,237 research outputs found
The effect of filler loading ratios and moisture on DC conductivity and space charge behaviour of SiO2 and hBN filled epoxy nanocomposites
No full textNanocomposites those exhibit good insulation properties have already attracted numbers of research and their electrical properties are believed to be related to charge dynamics in bulk of materials. However, it is still unclear on how nanofiller loading ratios, surface treatment and resultant changes in morphology influence the charge dynamics of nanocomposites. In this paper, we have clearly mentioned the influence of adding nanoparticles into epoxy resins and the characteristics of the movement of charges in the materials based on combining analysis on morphology, DC conductivity and space charge measurements. The presence of spherical nanoparticles (SiO2) introduced additional traps in bulk, which impaired the charge injection and reduced the mobility of charge carriers in samples of low filler loading ratios (e.g., 0.5 wt%). However, in silica-based samples of higher filler loadings, more nanoparticles further caused a higher density of traps, which resulted in lower average distance between arbitrary traps/ inter-particle surface distances and thus charge carriers required less energy when moving from one to another by hopping or the quantum tunnelling mechanism. The surface treatment of SiO2 particles introduced deep traps which helped the separation of particles or related traps, and to some extent restricted the transport of charge carriers. In addition, hBN particles seem to act as barriers to charge injection and movement due to the layered structures and large numbers of resultant shallow traps in bulk. In term of moisture effect, the presence of water led to an obvious increase in charge injection and mobility, and resulted in the higher mobility of charge carriers in both base materials and within traps/particles of nanocomposites. The existence of water shells around spherical particles could contribute to a higher probability of the quantum tunnelling process and the formation of conductive percolation channels
Experimental study and numerical estimation of moisture effect on charge transport in polymer nanocomposites
No full textPolymer nanocomposites as dielectrics have attracted a wide range of research interests due to their improved performance. One of the observed characteristics of polymer nanocomposites is the suppression on space charge injection and accumulation and the charge transport mechanism behind is also investigated based on thermally activated hopping (TAH) and quantum mechanical tunnelling (QMT) mechanisms. However, there still lacks research on the effect of moisture on charge transport characteristics and its relationship with experimental results. We herein proposed a method to re-virtualize the distribution of nanoparticles/their aggregates based on the multidimensional scaling (MDS) method in the first step, and a simple numerical method is further following to estimate the contribution of TAH and QMT conductivities to the experimental ones. The results, firstly, indicate the presence of moisture could lead to significant charge injections, and for different relative humidity conditions, due to their diverse water shell thickness, the separation distances of nanoparticles where deep/shallow traps locate show an obvious reduction and consequently vary the contribution of TAH and QMT conductivities in the measured ones. Second, the TAH mechanism plays the main role in charge transport/conduction, especially under lower RH conditions, while the obvious increment of QMT conduction is attributed to the reduced trap distances caused by thicker conductive water shells and support the existence of deep traps. Besides, the proposed model could be potentially extended to other research topics on electrical properties of polymer nanocomposites, such as particle size, dispersion/distribution status and filler loading concentrations which can be reflected and explained via the variation of nanoparticle surface/trap site distances
Thermal stability of epoxy nanocomposites: surface treatment and morphology impact based on nano SiO2 and hBN fillers
No full textEpoxy resin is one of the most commonly used thermosetting macromolecular synthetic materials. It displays excellent adhesiveness properties, good dielectric property, mechanical property and chemical stability. Consequently, epoxy resins have been widely used for many industrial purposes, such as electrical casting into power transformers, ignition coil systems and potting. In this paper, TGA and DSC measurements were carried out to evaluate the thermal stability of epoxy nanocomposites. Based on the results of dispersion and distribution of particles within epoxy nanocomposites, it concluded that both presences of nano SiO2 and hexagonal BN (hBN) particles have obvious impact on base materials in which the influences of latter particle are much more significant due to its shape, and thus both fillers leads to worse thermal stability than pure samples. However, particles could act as flame retardants in polymer nanocomposites and postpone the initiation of decomposition by hindering/slowing the oxidisation. When compared within two SiO2 based nanocomposites, the surface treatment seems to help mitigate the influences on base materials by achieving better filler dispersion and modify the cross-linking density at the interfacial areas by removing surface functional groups
Using performance assessment in secondary school mathematics: an empirical study in a Singapore classroom
No full textThis article reports an exploratory study on using performance assessment in mathematics instruction in a high-performing secondary school in Singapore. An intact mathematics class participated in the study, and received chapter-based performance tasks as intervention during regular mathematics lessons for about one and a half school years. The performance tasks used included authentic and/or open-ended tasks. The students’ academic achievements and attitudes in mathematics were compared with a comparison class that did not receive the intervention. Both quantitative and qualitative data were collected, mainly through questionnaire surveys, performance task tests, conventional school exams, and interviews with students and teachers. The results suggest that the students receiving the intervention performed significantly better than their counterparts in solving conventional exam problems, and in general they also showed more positive changes in attitudes towards mathematics and mathematics learning. The students from the experimental class also expressed positive views about the benefits of using performance tasks in promoting their ability in higher order thinking, though no statistically significant difference was detected between the two classes of students in solving unconventional tasks before and after intervention. Overall, the results appear to support teachers’ using contextualised problems in real life situations and open-ended investigations in students’ learning of mathematic
sj-docx-1-cpc-10.1177_10556656231184966 - Supplemental material for Reliability and Validity of the CLEFT-Q in a Chinese Context
No full textSupplemental material, sj-docx-1-cpc-10.1177_10556656231184966 for Reliability and Validity of the CLEFT-Q in a Chinese Context by Yuzhe Ding, Wenying Kuang, Xinyu Zhang, Wenjuan Zhang, Jingyi Xu, Jianan Yan, Yanyu Guo, Jie Zheng and Wenjun Yuan in The Cleft Palate Craniofacial Journal</p
Appendix_B – Supplemental material for Trends in Diabetes Mortality by Gender in Urban and Rural Areas in China From 2003 to 2012: An Age-Period-Cohort Analysis
No full textSupplemental material, Appendix_B for Trends in Diabetes Mortality by Gender in Urban and Rural Areas in China From 2003 to 2012: An Age-Period-Cohort Analysis by Yuanyuan Li, Changgui Kou, Wei Bai, Wanqing Hua, Weiying Yu, Yan Song, Xinyu Liu and Wenjun Li in Asia Pacific Journal of Public Health</p
Appendix_A – Supplemental material for Trends in Diabetes Mortality by Gender in Urban and Rural Areas in China From 2003 to 2012: An Age-Period-Cohort Analysis
No full textSupplemental material, Appendix_A for Trends in Diabetes Mortality by Gender in Urban and Rural Areas in China From 2003 to 2012: An Age-Period-Cohort Analysis by Yuanyuan Li, Changgui Kou, Wei Bai, Wanqing Hua, Weiying Yu, Yan Song, Xinyu Liu and Wenjun Li in Asia Pacific Journal of Public Health</p
sj-docx-2-cpc-10.1177_10556656231184966 - Supplemental material for Reliability and Validity of the CLEFT-Q in a Chinese Context
No full textSupplemental material, sj-docx-2-cpc-10.1177_10556656231184966 for Reliability and Validity of the CLEFT-Q in a Chinese Context by Yuzhe Ding, Wenying Kuang, Xinyu Zhang, Wenjuan Zhang, Jingyi Xu, Jianan Yan, Yanyu Guo, Jie Zheng and Wenjun Yuan in The Cleft Palate Craniofacial Journal</p
sj-docx-3-cpc-10.1177_10556656231184966 - Supplemental material for Reliability and Validity of the CLEFT-Q in a Chinese Context
No full textSupplemental material, sj-docx-3-cpc-10.1177_10556656231184966 for Reliability and Validity of the CLEFT-Q in a Chinese Context by Yuzhe Ding, Wenying Kuang, Xinyu Zhang, Wenjuan Zhang, Jingyi Xu, Jianan Yan, Yanyu Guo, Jie Zheng and Wenjun Yuan in The Cleft Palate Craniofacial Journal</p
sj-docx-4-cpc-10.1177_10556656231184966 - Supplemental material for Reliability and Validity of the CLEFT-Q in a Chinese Context
No full textSupplemental material, sj-docx-4-cpc-10.1177_10556656231184966 for Reliability and Validity of the CLEFT-Q in a Chinese Context by Yuzhe Ding, Wenying Kuang, Xinyu Zhang, Wenjuan Zhang, Jingyi Xu, Jianan Yan, Yanyu Guo, Jie Zheng and Wenjun Yuan in The Cleft Palate Craniofacial Journal</p
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