Biomineralization studies on cellulose membrane exposed to biological fluids of Anodonta cygnea

The present work proposes to analyse the results obtained under in vitro conditions where cellulose artificial membranes were incubated with biological fluids from the freshwater bivalve Anodonta cygnea. The membranes were mounted between two half ‘Ussing chambers’ with different composition solutions in order to simulate epithelial surfaces separating organic fluid compartments. The membrane surfaces were submitted to two synthetic calcium and phosphate solutions on opposite sides, at pH 6.0, 7.0 or 9.0 during a period of 6 hours. Additional assays were accomplished mixing these solutions with haemolymph or extrapallial fluid from A. cygnea, only on the calcium side. A selective ion movement, mainly dependent on the membrane pore size and/or cationic affinity, occurred with higher permeability for calcium ions to the opposite phosphate chamber supported by calcium diffusion forces across the cellulose membrane. In general, this promoted a more intense mineral precipitation on the phosphate membrane surface. A strong deposition of calcium phosphate mineral was observed at pH 9.0 as a primary layer with a homogeneous microstructure, being totally absent at pH 6.0. The membrane showed an additional crystal phase at pH 7.0 exhibiting a very particular hexagonal or cuttlebone shape, mainly on the phosphate surface. When organic fluids of A. cygnea were included, these crystal forms presented a high tendency to aggregate under rosaceous shapes, also predominantly in the phosphate side. The cellulose membrane was permeable to small organic molecules that diffused from the calcium towards the phosphate side. In the calcium side, very few similar crystals were observed. The presence of organic matrix from A. cygnea fluids induced a preliminary apatite–brushite crystal polymorphism. So, the present results suggest that cellulose membranes can be used as surrogates of biological epithelia with preferential ionic diffusion from the calcium to the phosphate side where the main mineral precipitation events occurred. Additionally, the organic fluids from freshwater bivalves should be also thoroughly researched in the applied biomedical field, as mineral nucleators and crystal modulators on biosynthetic systems

The effect of weekly quizzes on the development of students' theoretical thinking

In this thesis, we evaluate the effectiveness of a basic tool for the teaching of linear algebra at university level: the administration of weekly quizzes. These tests, each made of two short, conceptual questions, are believed to have the potential of developing students' theoretical thinking. At the start of our research we believed that this kind of thinking is necessary for the understanding of linear algebra and that it represents, in general, an important educational aim in university teaching. To see if, indeed, the quizzes can contribute to the development of students' theoretical thinking, we have analyzed students' solutions to the weekly quizzes administered in a Linear Algebra II course at Concordia University in Montreal, over a one-semester time span. We have used, for this purpose, a model of thinking that characterizes theoretical thinking by certain properties, which contrast practical and theoretical thinking. Our study shows that the administration of weekly quizzes could not account for the development, in general, of theoretical thinking, with all the characteristics that it encompasses. We have found that the group's engagement with certain features of thinking is directly influenced by the mathematical content of the questions in the quizzes, and thus it is impossible to evaluate their development in time. However, the quizzes do have the potential of developing other features of theoretical thinking, that we have called, more generally "habits of the mind", because they are less conditioned by content specificities

Teaching fractions through a Measurement Approach to prospective elementary teachers: A design experiment in a Math Methods course

In this study we give an account of a teaching experiment on fractions to prospective elementary teachers, which took place in winter 2014 in a Teaching Mathematics course in an Elementary Education undergraduate program at a North-American university. The experiment was an adaptation for teacher education of the “Measurement Approach” to teaching fractions developed by the psychologist V.V. Davydov for the elementary mathematics curriculum (Davydov & Tsvetkovich, 1991). The research had the characteristics of a design experiment, with a phase of reflection on the sources of meaning of fractions appropriate for the elementary school, as well as preliminary trials with one year before (winter 2013) preceding the implementation of the experiment in a “mature form.” We had two overarching goals in the design conception: fostering future teachers’ quantitative reasoning and cultivating a positioning relative to the course institution that is more conducive to accepting the approach – that of university students acquiring theoretical knowledge. In the description and the retrospective analysis of the teaching intervention we follow the realization of these goals at three levels: the overall organization of the material and tasks in the course by the instructor, the classroom interactions between the instructor and the students in lectures, and individual reasoning without mediation by the instructor. We found that the Measurement Approach encouraged a culture of systemic justification in the classroom with some students adopting flexibly and creatively the proposed models of reasoning within a given theory. However, the risk of students’ imitating only certain aspects of these models – such as words, sentence structures, or procedures – ran high, with many students using the theory only as “decoration”, without adequate understanding. Furthermore, although spontaneous engagement with quantitative reasoning for establishing validity of statements about fractions or for explaining realistic problems was rare, it was present in several students, in encouraging forms. Very few students adopted such reasoning, but those who did, exhibited sophisticated and varied strategies for solving problems, which demonstrated robust understanding of the fraction of quantity theory

Teaching fractions through a Measurement Approach to prospective elementary teachers: A design experiment in a Math Methods course

In this study we give an account of a teaching experiment on fractions to prospective elementary teachers, which took place in winter 2014 in a Teaching Mathematics course in an Elementary Education undergraduate program at a North-American university. The experiment was an adaptation for teacher education of the “Measurement Approach” to teaching fractions developed by the psychologist V.V. Davydov for the elementary mathematics curriculum (Davydov & Tsvetkovich, 1991). The research had the characteristics of a design experiment, with a phase of reflection on the sources of meaning of fractions appropriate for the elementary school, as well as preliminary trials with one year before (winter 2013) preceding the implementation of the experiment in a “mature form.” We had two overarching goals in the design conception: fostering future teachers’ quantitative reasoning and cultivating a positioning relative to the course institution that is more conducive to accepting the approach – that of university students acquiring theoretical knowledge. In the description and the retrospective analysis of the teaching intervention we follow the realization of these goals at three levels: the overall organization of the material and tasks in the course by the instructor, the classroom interactions between the instructor and the students in lectures, and individual reasoning without mediation by the instructor. We found that the Measurement Approach encouraged a culture of systemic justification in the classroom with some students adopting flexibly and creatively the proposed models of reasoning within a given theory. However, the risk of students’ imitating only certain aspects of these models – such as words, sentence structures, or procedures – ran high, with many students using the theory only as “decoration”, without adequate understanding. Furthermore, although spontaneous engagement with quantitative reasoning for establishing validity of statements about fractions or for explaining realistic problems was rare, it was present in several students, in encouraging forms. Very few students adopted such reasoning, but those who did, exhibited sophisticated and varied strategies for solving problems, which demonstrated robust understanding of the fraction of quantity theory

Políticas Públicas no Contexto de Riscos Políticos, Militares e Financeiros: Desafios e Formas de Implementação

The purpose of article is to provide a comprehensive analysis of the main challenges and opportunities for implementing public policy in the context of political, military, and financial instability. The study is based on qualitative approach, using expert opinions, literature analysis, and review articles for a comprehensive understanding of risks and their impact on public policies. The main emphasis is placed on the content analysis of literature sources, which allows for a broader understanding of the public policy phenomenon. The results demonstrate that the ability of the system to effectively regulate and anticipate conflicts and crises significantly affects the country’s domestic and foreign policy course, as well as the effectiveness of political governance. The authors emphasise that political conflicts, as an integral part of political life, determine the nature of public space and interaction between the government and society. The results of the study indicate a significant impact of geopolitical crises on the internal affairs of the country and the need to adapt public policy to new conditions. The emphasis is placed on the role of the authorities in ensuring sustainable development and a decisive response to challenges of risky environment. The conclusions determine that effective solution of complex public policy tasks in the context of risks requires a comprehensive approach, involvement of civil society, partnerships between the government and citizens. The article emphasises the importance of democratic principles, decentralisation, and international cooperation as key factors for the successful implementation of public policy in the context of heightened risks.O objetivo deste artigo é fornecer análise abrangente dos principais desafios e oportunidades para a implementação políticas públicas num contexto de instabilidade política, militar e financeira. O estudo baseia-se numa abordagem qualitativa, recorrendo a opiniões de especialistas, análise literatura artigos de revisão para uma compreensão abrangente dos riscos e do seu impacto nas políticas públicas. A ênfase principal é colocada na análise de conteúdo das fontes bibliográficas, permite uma compreensão mais ampla do fenómeno das políticas públicas. Os autores sublinham que os conflitos políticos, enquanto parte integrante da vida política, determinam a natureza do espaço público e a interação entre o governo e a sociedade. À medida que o entendimento de política pública alargado a diferentes actores, a identificação de mecanismos de conciliação de interesses torna-se um processo multicomponente que depende de vários factores, como a natureza do regime, o funcionamento das instituições e as tradições culturais da sociedade. Os resultados estudo indicam impacto significativo das crises geopolíticas nos assuntos internos necessidade de adaptar as políticas públicas às novas condições. A tónica é colocada no papel das autoridades para assegurar o desenvolvimento sustentável resposta decisiva aos desafios de um ambiente de risco. As conclusões determinam que a solução efectiva de tarefas complexas de política pública no contexto de riscos exige uma abordagem abrangente, o envolvimento da sociedade civil e parcerias entre o governo cidadãos. O artigo sublinha a importância dos princípios democráticos, da descentralização cooperação internacional como factores-chave êxito da aplicação das políticas públicas no contexto de riscos acrescidos