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1.
2.
Raquel Rodríguez 《Polymer》2008,49(3):691-696
The limiting conversion phenomenon observed in high solid content silicone-modified acrylic miniemulsion polymerizations was investigated. It was found that the limiting conversion was mainly due to the formation of inactive radicals upon propagation of butyl acrylate radicals with the vinyl end groups of the polydimethylsiloxane. Polymerization strategies that allowed overcoming this problem and achieving high monomer conversion were implemented. 相似文献
3.
Raquel Alves dos Santos Teresinha Rosa Cabral Isabel Rosa Cabral Lusania Maria Greggi Antunes Cristiane Pontes Andrade Plínio Cerqueira dos Santos Cardoso Marcelo de Oliveira Bahia Claudia Pessoa José Luis Martins do Nascimento Rommel Rodríguez Burbano Catarina Satie Takahashi 《Biocell》2008,32(2):195-200
Physalis angulata L (Solanaceae) is a medicinal plant from North of Brazil, whose different extracts and infusions are commonly used in the popular medicine for the treatment of malaria, asthma, hepatitis, dermatitis and rheumatism. However, the genotoxic effects of P. angulata on human cells is not well known. The main purpose of the present study was to evaluate the in vitro genotoxic effects of aqueous extract of P. angulata using the comet assay and the micronucleus assay in human lymphocytes provided from 6 healthy donors. Treatments with P. angulata extracts were performed in vitro in order to access the extent of DNA damage. The comet assay has shown that treatments with P. angulata at 0.5, 1.0, 2.0, 3.0 and 6.0 microg/mL in culture medium were genotoxic. Lymphocytes treated with P. angulata at the concentrations of 3.0 and 6.0 microg/mL in culture medium showed a statistically significant increase in the frequency of micronucleus (p<0.05), however, the cytokinesis blocked proliferation index (CBPI) was not decreased after P. angulata treatment. In conclusion, the present work demonstrated the genotoxic effects of P. angulata extract on human lymphocytes in vitro. 相似文献
4.
Exfoliation and related microstructures in 2024 aluminum body skins on aging aircraft 总被引:3,自引:0,他引:3
Maria Posada L. E. Murr C. -S. Niou D. Roberson D. Little Roy Arrowood Debra George 《Materials Characterization》1997,38(4-5):259-272
Exfoliation, a directional attack along elongated grain boundaries, has been examined in some detail in rolled 2024 aluminum sheet and plate for KC-135 aging aircraft body skin samples utilizing optical (light) metallography, scanning electron microscopy, and transmission electron microscopy. A detailed analysis and comparison of precipitates within the grains and in the grain boundaries were performed, as well as an examination of elemental depletion profiles across grain boundaries. These observations suggest that corrosion-related anodic sites play a far less significant role in the propagation of exfoliation than do the hard corrosion products creating wedging stresses within the elongated grain boundaries, which seem to demonstrate unique and unusual structural or energetic features or both. 相似文献
5.
Posada J.F. Liou J.J. Miller R.N. 《IEEE transactions on instrumentation and measurement》1991,40(5):836-841
Population growth results in an increasing demand on water supply. Usually, growers determine how much water is needed to irrigate their fields on the basis of the amount of time elapsed since the last irrigation cycle. A soil moisture sensor enables the users (or an automated irrigation system) to monitor the relative soil moisture constantly at many different locations throughout the field in order to schedule irrigation cycles more precisely. An automated data acquisition system for measuring the characteristics of a soil moisture sensor under various moisture conditions is presented. Based on the measurement data, an empirical model for the soil moisture sensor is also developed. A comparison of the model and experimental data is included 相似文献
6.
Blends of isotactic polypropylene (PP), ethylene‐propylene rubber copolymer (EPR), and ethylene‐propylene crystalline copolymer (EPC) can be produced through in situ polymerization processes directly in the reactor and blends with different structure and composition can be obtained. In this work we studied the structure of five reactor‐made blends of PP, EPR, and EPC produced by a Ziegler‐Natta catalyst system. The composition of EPR was related to the ratio between ethylene and propylene used in the copolymerization step. The ethylene content in the EPR was in the range of 50–70 mol %. The crystallization behavior of PP and EPC in the blends was influenced by the presence of the rubber, and some specific interactions between the components could be established. By preparative temperature rising elution fractionation (P‐TREF) analysis, the isolation and characterization of crystalline EPC fractions were made. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2155–2162, 2004 相似文献
7.
Raquel Santos Mauler Fernando Guaragna Martins Dimitrios Samios 《Polymer Bulletin》1995,35(1-2):151-156
Summary The cleavage of styrene-butadiene rubber (SBR) with periodic acid (H5IO6) and simultaneous injection of ultrasonic radiation has been performed. Two frequencies, 25 and 40 kHz, respectively, have been used. The results demonstrate clearly that 40 kHz ultrasound radiation accelerates significantly the cleavage reaction. The Pearl String Model theory had been used to elucidate this process. 相似文献
8.
MXene Yarn Supercapacitors: High‐Performance Biscrolled MXene/Carbon Nanotube Yarn Supercapacitors (Small 37/2018) 下载免费PDF全文
9.
Raquel Benbunan-Fich Marios Koufaris 《Information Systems and E-Business Management》2010,8(2):131-148
Given the continuous growth of social bookmarking sites, we investigated the reasons behind their sustainability as online
social structures. Bookmarking sites offer users the option to post and tag web resources privately or to make them publicly
available to other users of the sites. A prevalence of private tagging would threaten the sustainability of the social aspects
at these sites. Using activity data from a sample of 1,000 users of Simpy, a popular social bookmarking site, we found that
the majority of users contribute most of their tagged resources to the public repository, despite the option to keep them
private. We also found that in social bookmarking sites there is a minority of extremely prolific contributors who are responsible
for a large portion of public tagged resources. Finally, we found that new users make larger proportions of their contributions
public than existing users and that there is a larger number of regular contributors to the site than irregular ones. All
of these findings are consistent with the mechanisms predicted by a theoretical model of sustainable online social structures. 相似文献
10.
Diana Pérez-Marín Raquel Hijón-Neira Liliana Santacruz 《Behaviour & Information Technology》2016,35(7):572-585
According to active learning, students should be responsible for their own learning. Automatic free-text scoring allows teachers to provide open-ended questions with their correct answers to a computer system, so when students answer the questions, they get immediate feedback (a score, a comment, or both). However, teachers are usually overloaded with many tasks, and they may not have time to create the questions with the correct answers. Therefore, in the 2012/2013 academic year, we asked a group of 124 Pre-Primary and Primary Education students to become the creators of the questions and their correct answers in groups in a free-text scoring system, so the questions use learners’ language, not teachers’ language. From them, 41 students (group of involved students, GIS) fulfilled all the requirements during the course. Our hypothesis was that GIS would be able to increase their academic performance and levels of engagement compared to the rest of the students. The results gathered provide statistic evidence to support that hypothesis. This study pretends to help teachers who want to increase the academic performance and levels of engagement of their students in courses that they may find boring and unrelated to the main topic of their degree, or not directly related with their main academic interests. 相似文献